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How to Solve Any Physics Problem

Last Updated: July 21, 2023 Fact Checked

This article was co-authored by Sean Alexander, MS . Sean Alexander is an Academic Tutor specializing in teaching mathematics and physics. Sean is the Owner of Alexander Tutoring, an academic tutoring business that provides personalized studying sessions focused on mathematics and physics. With over 15 years of experience, Sean has worked as a physics and math instructor and tutor for Stanford University, San Francisco State University, and Stanbridge Academy. He holds a BS in Physics from the University of California, Santa Barbara and an MS in Theoretical Physics from San Francisco State University. This article has been fact-checked, ensuring the accuracy of any cited facts and confirming the authority of its sources. This article has been viewed 329,393 times.

Baffled as to where to begin with a physics problem? There is a very simply and logical flow process to solving any physics problem.

Step 1 Calm down.

  • Ask yourself if your answers make sense. If the numbers look absurd (for example, you get that a rock dropped off a 50-meter cliff moves with the speed of only 0.00965 meters per second when it hits the ground), you made a mistake somewhere.
  • Don't forget to include the units into your answers, and always keep track of them. So, if you are solving for velocity and get your answer in seconds, that is a sign that something went wrong, because it should be in meters per second.
  • Plug your answers back into the original equations to make sure you get the same number on both sides.

Step 10 Put a box, circle, or underline your answer to make your work neat.

Community Q&A

Community Answer

  • Many people report that if they leave a problem for a while and come back to it later, they find they have a new perspective on it and can sometimes see an easy way to the answer that they did not notice before. Thanks Helpful 249 Not Helpful 48
  • Try to understand the problem first. Thanks Helpful 186 Not Helpful 51
  • Remember, the physics part of the problem is figuring out what you are solving for, drawing the diagram, and remembering the formulae. The rest is just use of algebra, trigonometry, and/or calculus, depending on the difficulty of your course. Thanks Helpful 115 Not Helpful 34

what is problem solving in physics

  • Physics is not easy to grasp for many people, so do not get bent out of shape over a problem. Thanks Helpful 100 Not Helpful 25
  • If an instructor tells you to draw a free body diagram, be sure that that is exactly what you draw. Thanks Helpful 89 Not Helpful 24

Things You'll Need

  • A Writing Utensil (preferably a pencil or erasable pen of sorts)
  • Calculator with all the functions you need for your exam
  • An understanding of the equations needed to solve the problems. Or a list of them will suffice if you are just trying to get through the course alive.

You Might Also Like

Convert Kelvin to Fahrenheit or Celsius

Expert Interview

what is problem solving in physics

Thanks for reading our article! If you’d like to learn more about teaching, check out our in-depth interview with Sean Alexander, MS .

  • ↑ https://iopscience.iop.org/article/10.1088/1361-6404/aa9038
  • ↑ https://physics.wvu.edu/files/d/ce78505d-1426-4d68-8bb2-128d8aac6b1b/expertapproachtosolvingphysicsproblems.pdf
  • ↑ https://www.brighthubeducation.com/science-homework-help/42596-tips-to-choosing-the-correct-physics-formula/

About This Article

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4.6 Problem-Solving Strategies

Learning objectives.

By the end of this section, you will be able to:

  • Understand and apply a problem-solving procedure to solve problems using Newton's laws of motion.

Success in problem solving is obviously necessary to understand and apply physical principles, not to mention the more immediate need of passing exams. The basics of problem solving, presented earlier in this text, are followed here, but specific strategies useful in applying Newton’s laws of motion are emphasized. These techniques also reinforce concepts that are useful in many other areas of physics. Many problem-solving strategies are stated outright in the worked examples, and so the following techniques should reinforce skills you have already begun to develop.

Problem-Solving Strategy for Newton’s Laws of Motion

Step 1. As usual, it is first necessary to identify the physical principles involved. Once it is determined that Newton’s laws of motion are involved (if the problem involves forces), it is particularly important to draw a careful sketch of the situation . Such a sketch is shown in Figure 4.20 (a). Then, as in Figure 4.20 (b), use arrows to represent all forces, label them carefully, and make their lengths and directions correspond to the forces they represent (whenever sufficient information exists).

Step 2. Identify what needs to be determined and what is known or can be inferred from the problem as stated. That is, make a list of knowns and unknowns. Then carefully determine the system of interest . This decision is a crucial step, since Newton’s second law involves only external forces. Once the system of interest has been identified, it becomes possible to determine which forces are external and which are internal, a necessary step to employ Newton’s second law. (See Figure 4.20 (c).) Newton’s third law may be used to identify whether forces are exerted between components of a system (internal) or between the system and something outside (external). As illustrated earlier in this chapter, the system of interest depends on what question we need to answer. This choice becomes easier with practice, eventually developing into an almost unconscious process. Skill in clearly defining systems will be beneficial in later chapters as well. A diagram showing the system of interest and all of the external forces is called a free-body diagram . Only forces are shown on free-body diagrams, not acceleration or velocity. We have drawn several of these in worked examples. Figure 4.20 (c) shows a free-body diagram for the system of interest. Note that no internal forces are shown in a free-body diagram.

Step 3. Once a free-body diagram is drawn, Newton’s second law can be applied to solve the problem . This is done in Figure 4.20 (d) for a particular situation. In general, once external forces are clearly identified in free-body diagrams, it should be a straightforward task to put them into equation form and solve for the unknown, as done in all previous examples. If the problem is one-dimensional—that is, if all forces are parallel—then they add like scalars. If the problem is two-dimensional, then it must be broken down into a pair of one-dimensional problems. This is done by projecting the force vectors onto a set of axes chosen for convenience. As seen in previous examples, the choice of axes can simplify the problem. For example, when an incline is involved, a set of axes with one axis parallel to the incline and one perpendicular to it is most convenient. It is almost always convenient to make one axis parallel to the direction of motion, if this is known.

Applying Newton’s Second Law

Before you write net force equations, it is critical to determine whether the system is accelerating in a particular direction. If the acceleration is zero in a particular direction, then the net force is zero in that direction. Similarly, if the acceleration is nonzero in a particular direction, then the net force is described by the equation: F net = ma F net = ma .

For example, if the system is accelerating in the horizontal direction, but it is not accelerating in the vertical direction, then you will have the following conclusions:

You will need this information in order to determine unknown forces acting in a system.

Step 4. As always, check the solution to see whether it is reasonable . In some cases, this is obvious. For example, it is reasonable to find that friction causes an object to slide down an incline more slowly than when no friction exists. In practice, intuition develops gradually through problem solving, and with experience it becomes progressively easier to judge whether an answer is reasonable. Another way to check your solution is to check the units. If you are solving for force and end up with units of m/s, then you have made a mistake.

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How To Solve Physics Problems

Proper problem-solving techniques not only help guide you through the difficulties of a problem but also enable you to communicate your solution effectively to others. When working out solutions to problems in this course, please bear the following points in mind.

. Near the diagram, draw up a table of the givens, being sure to respect the precision and units given in the problem statement.

. Outline the final (rounded) answer written . An answer of 1.0 x 10 s should often be converted to 120 days or 3.8 months to make the answer more meaningful or useful. In subsequent calculations, use unrounded values and round at the end.

Object weighs 94.0 lb and object weighs 29.0 lb. Between object and the plane the coefficient of static friction is 0.56 and coefficient of kinetic friction is 0.25. ( ) Find the acceleration of the system if is initially at rest. ( ) Find the acceleration if is moving up the plane. ( ) What is the acceleration if is moving down the plane? The plane is inclined by 42.0°.

From the force diagram for , we get the equation

, we get the pair of equations

, for the object to remain at rest. Let us calculate assuming the objects remain at rest to determine whether this is less than the given value. Substituting < , the objects remain at rest.

(b) If is initially moving up the plane, then the sense of the frictional force is opposite to that indicated in the diagram. We can solve for either case by writing the third equation as

the plane, and the lower sign to motion the plane. Solving for the acceleration gives

= 32.2 ft s-2 gives


This page was last modified on Fri, Aug 29, 1997.

Dynamics: Force and Newton’s Laws of Motion

Problem-solving strategies, learning objective.

By the end of this section, you will be able to:

  • Understand and apply a problem-solving procedure to solve problems using Newton’s laws of motion.

Success in problem solving is obviously necessary to understand and apply physical principles, not to mention the more immediate need of passing exams. The basics of problem solving, presented earlier in this text, are followed here, but specific strategies useful in applying Newton’s laws of motion are emphasized. These techniques also reinforce concepts that are useful in many other areas of physics. Many problem-solving strategies are stated outright in the worked examples, and so the following techniques should reinforce skills you have already begun to develop.

Problem-Solving Strategy for Newton’s Laws of Motion

Step 1. As usual, it is first necessary to identify the physical principles involved. Once it is determined that Newton’s laws of motion are involved (if the problem involves forces), it is particularly important to draw a careful sketch of the situation . Such a sketch is shown in Figure 1(a). Then, as in Figure 1(b), use arrows to represent all forces, label them carefully, and make their lengths and directions correspond to the forces they represent (whenever sufficient information exists).

Figure 1. (a) A sketch of Tarzan hanging from a vine. (b) Arrows are used to represent all forces. T is the tension in the vine above Tarzan, F T is the force he exerts on the vine, and w is his weight. All other forces, such as the nudge of a breeze, are assumed negligible. (c) Suppose we are given the ape man’s mass and asked to find the tension in the vine. We then define the system of interest as shown and draw a free-body diagram. F T is no longer shown, because it is not a force acting on the system of interest; rather, F T  acts on the outside world. (d) Showing only the arrows, the head-to-tail method of addition is used. It is apparent that T = –w , if Tarzan is stationary.

Step 2. Identify what needs to be determined and what is known or can be inferred from the problem as stated. That is, make a list of knowns and unknowns. Then carefully determine the system of interest . This decision is a crucial step, since Newton’s second law involves only external forces. Once the system of interest has been identified, it becomes possible to determine which forces are external and which are internal, a necessary step to employ Newton’s second law. (See Figure 1(c).) Newton’s third law may be used to identify whether forces are exerted between components of a system (internal) or between the system and something outside (external). As illustrated earlier in this chapter, the system of interest depends on what question we need to answer. This choice becomes easier with practice, eventually developing into an almost unconscious process. Skill in clearly defining systems will be beneficial in later chapters as well.

A diagram showing the system of interest and all of the external forces is called a free-body diagram . Only forces are shown on free-body diagrams, not acceleration or velocity. We have drawn several of these in worked examples. Figure 1(c) shows a free-body diagram for the system of interest. Note that no internal forces are shown in a free-body diagram.

Step 3. Once a free-body diagram is drawn, Newton’s second law can be applied to solve the problem . This is done in Figure 1(d) for a particular situation. In general, once external forces are clearly identified in free-body diagrams, it should be a straightforward task to put them into equation form and solve for the unknown, as done in all previous examples. If the problem is one-dimensional—that is, if all forces are parallel—then they add like scalars. If the problem is two-dimensional, then it must be broken down into a pair of one-dimensional problems. This is done by projecting the force vectors onto a set of axes chosen for convenience. As seen in previous examples, the choice of axes can simplify the problem. For example, when an incline is involved, a set of axes with one axis parallel to the incline and one perpendicular to it is most convenient. It is almost always convenient to make one axis parallel to the direction of motion, if this is known.

Applying Newton’s Second Law

image

F net x  = ma ,

F net y = 0.

You will need this information in order to determine unknown forces acting in a system.

Step 4. As always, check the solution to see whether it is reasonable . In some cases, this is obvious. For example, it is reasonable to find that friction causes an object to slide down an incline more slowly than when no friction exists. In practice, intuition develops gradually through problem solving, and with experience it becomes progressively easier to judge whether an answer is reasonable. Another way to check your solution is to check the units. If you are solving for force and end up with units of m/s, then you have made a mistake.

Section Summary

To solve problems involving Newton’s laws of motion, follow the procedure described:

  • Draw a sketch of the problem.
  • Identify known and unknown quantities, and identify the system of interest. Draw a free-body diagram, which is a sketch showing all of the forces acting on an object. The object is represented by a dot, and the forces are represented by vectors extending in different directions from the dot. If vectors act in directions that are not horizontal or vertical, resolve the vectors into horizontal and vertical components and draw them on the free-body diagram.
  • Write Newton’s second law in the horizontal and vertical directions and add the forces acting on the object. If the object does not accelerate in a particular direction (for example, the x-direction) then  F net x  = 0 . If the object does accelerate in that direction,  F net x  = ma .
  • Check your answer. Is the answer reasonable? Are the units correct?

Problems & Exercises

1. A 5.00 × 10 5 -kg rocket is accelerating straight up. Its engines produce 1.250 × 10 7  of thrust, and air resistance is 4.50 × 10 6 N. What is the rocket’s acceleration? Explicitly show how you follow the steps in the Problem-Solving Strategy for Newton’s laws of motion.

2. The wheels of a midsize car exert a force of 2100 N backward on the road to accelerate the car in the forward direction. If the force of friction including air resistance is 250 N and the acceleration of the car is 1.80 m/s 2 , what is the mass of the car plus its occupants? Explicitly show how you follow the steps in the Problem-Solving Strategy for Newton’s laws of motion. For this situation, draw a free-body diagram and write the net force equation.

3. Calculate the force a 70.0-kg high jumper must exert on the ground to produce an upward acceleration 4.00 times the acceleration due to gravity. Explicitly show how you follow the steps in the Problem-Solving Strategy for Newton’s laws of motion.

4. When landing after a spectacular somersault, a 40.0-kg gymnast decelerates by pushing straight down on the mat. Calculate the force she must exert if her deceleration is 7.00 times the acceleration due to gravity. Explicitly show how you follow the steps in the Problem-Solving Strategy for Newton’s laws of motion.

5. A freight train consists of two 8.00 × 10 4   engines and 45 cars with average masses of 5.50 × 10 4 kg . (a) What force must each engine exert backward on the track to accelerate the train at a rate of 5.00 × 10 -2  if the force of friction is 7.50 × 10 5 , assuming the engines exert identical forces? This is not a large frictional force for such a massive system. Rolling friction for trains is small, and consequently trains are very energy-efficient transportation systems. (b) What is the force in the coupling between the 37th and 38th cars (this is the force each exerts on the other), assuming all cars have the same mass and that friction is evenly distributed among all of the cars and engines?

6. Commercial airplanes are sometimes pushed out of the passenger loading area by a tractor. (a) An 1800-kg tractor exerts a force of 1.75 × 10 5  backward on the pavement, and the system experiences forces resisting motion that total 2400 N. If the acceleration is 0.150 m/s 2 , what is the mass of the airplane? (b) Calculate the force exerted by the tractor on the airplane, assuming 2200 N of the friction is experienced by the airplane. (c) Draw two sketches showing the systems of interest used to solve each part, including the free-body diagrams for each.

7. A 1100-kg car pulls a boat on a trailer. (a) What total force resists the motion of the car, boat, and trailer, if the car exerts a 1900-N force on the road and produces an acceleration of 0.550 m/s 2 ? The mass of the boat plus trailer is 700 kg. (b) What is the force in the hitch between the car and the trailer if 80% of the resisting forces are experienced by the boat and trailer?

8. (a) Find the magnitudes of the forces F 1 and F 2  that add to give the total force F tot  shown in Figure 4. This may be done either graphically or by using trigonometry. (b) Show graphically that the same total force is obtained independent of the order of addition of   F 1 and F 2 . (c) Find the direction and magnitude of some other pair of vectors that add to give F tot . Draw these to scale on the same drawing used in part (b) or a similar picture.

A right triangle is shown made up of three vectors. The first vector, F sub one, is along the triangle’s base toward the right; the second vector, F sub two, is along the perpendicular side pointing upward; and the third vector, F sub tot, is along the hypotenuse pointing up the incline. The magnitude of F sub tot is twenty newtons. In a free-body diagram, F sub one is shown by an arrow pointing right and F sub two is shown by an arrow acting vertically upward.

9. Two children pull a third child on a snow saucer sled exerting forces  F 1 and F 2 as shown from above in Figure 4 . Find the acceleration of the 49.00-kg sled and child system. Note that the direction of the frictional force is unspecified; it will be in the opposite direction of the sum of  F 1 and F 2 .

An overhead view of a child sitting on a snow saucer sled. Two forces, F sub one equal to ten newtons and F sub two equal to eight newtons, are acting toward the right. F sub one makes an angle of forty-five degrees from the x axis and F sub two makes an angle of thirty degrees from the x axis in a clockwise direction. A friction force f is equal to seven point five newtons, shown by a vector pointing in negative x direction. In the free-body diagram, F sub one and F sub two are shown by arrows toward the right, making a forty-five degree angle above the horizontal and a thirty-degree angle below the horizontal respectively. The friction force f is shown by an arrow along the negative x axis.

10. Suppose your car was mired deeply in the mud and you wanted to use the method illustrated in Figure 6 to pull it out. (a) What force would you have to exert perpendicular to the center of the rope to produce a force of 12,000 N on the car if the angle is 2.00°? In this part, explicitly show how you follow the steps in the Problem-Solving Strategy for Newton’s laws of motion. (b) Real ropes stretch under such forces. What force would be exerted on the car if the angle increases to 7.00° and you still apply the force found in part (a) to its center?

Figure of car stuck in the mud and a rope connected to a tree trunk in an attempt to pull out the car.

11. What force is exerted on the tooth in Figure 7 if the tension in the wire is 25.0 N? Note that the force applied to the tooth is smaller than the tension in the wire, but this is necessitated by practical considerations of how force can be applied in the mouth. Explicitly show how you follow steps in the Problem-Solving Strategy for Newton’s laws of motion.

Cross-section of jaw with sixteen teeth is shown. Braces are along the outside of the teeth. Three forces are acting on the protruding tooth. The applied force, F sub app, is shown by an arrow vertically downward; a second force, T, is shown by an arrow making an angle of fifteen degrees below the positive x axis; and a third force, T, is shown by an arrow making an angle of fifteen degrees below the negative x axis.

Figure 7. Braces are used to apply forces to teeth to realign them. Shown in this figure are the tensions applied by the wire to the protruding tooth. The total force applied to the tooth by the wire, F app , points straight toward the back of the mouth.

12. Figure 9 shows Superhero and Trusty Sidekick hanging motionless from a rope. Superhero’s mass is 90.0 kg, while Trusty Sidekick’s is 55.0 kg, and the mass of the rope is negligible. (a) Draw a free-body diagram of the situation showing all forces acting on Superhero, Trusty Sidekick, and the rope. (b) Find the tension in the rope above Superhero. (c) Find the tension in the rope between Superhero and Trusty Sidekick. Indicate on your free-body diagram the system of interest used to solve each part.

Two caped superheroes hang on a rope suspended vertically from a bar.

Figure 9. Superhero and Trusty Sidekick hang motionless on a rope as they try to figure out what to do next. Will the tension be the same everywhere in the rope?

13. A nurse pushes a cart by exerting a force on the handle at a downward angle 35.0º below the horizontal. The loaded cart has a mass of 28.0 kg, and the force of friction is 60.0 N. (a) Draw a free-body diagram for the system of interest. (b) What force must the nurse exert to move at a constant velocity?

14. Construct Your Own Problem Consider the tension in an elevator cable during the time the elevator starts from rest and accelerates its load upward to some cruising velocity. Taking the elevator and its load to be the system of interest, draw a free-body diagram. Then calculate the tension in the cable. Among the things to consider are the mass of the elevator and its load, the final velocity, and the time taken to reach that velocity.

15. Construct Your Own Problem Consider two people pushing a toboggan with four children on it up a snow-covered slope. Construct a problem in which you calculate the acceleration of the toboggan and its load. Include a free-body diagram of the appropriate system of interest as the basis for your analysis. Show vector forces and their components and explain the choice of coordinates. Among the things to be considered are the forces exerted by those pushing, the angle of the slope, and the masses of the toboggan and children.

16. Unreasonable Results (a) Repeat Exercise 7, but assume an acceleration of 1.20 m/s 2  is produced. (b) What is unreasonable about the result? (c) Which premise is unreasonable, and why is it unreasonable?

17. Unreasonable Results (a) What is the initial acceleration of a rocket that has a mass of 1.50 × 10 6  at takeoff, the engines of which produce a thrust of 2.00 × 10 6 ? Do not neglect gravity. (b) What is unreasonable about the result? (This result has been unintentionally achieved by several real rockets.) (c) Which premise is unreasonable, or which premises are inconsistent? (You may find it useful to compare this problem to the rocket problem earlier in this section.)

Selected Solutions to Problems & Exercises

1. Using the free-body diagram:

An object of mass m is shown. Three forces acting on it are tension T, shown by an arrow acting vertically upward, and friction f and gravity m g, shown by two arrows acting vertically downward.

  • [latex]{F}_{\text{net}}=T-f-mg=\text{ma}\\[/latex] ,

[latex]a=\frac{T-f-\text{mg}}{m}=\frac{1\text{.}\text{250}\times {\text{10}}^{7}\text{N}-4.50\times {\text{10}}^{\text{6}}N-\left(5.00\times {\text{10}}^{5}\text{kg}\right)\left(9.{\text{80 m/s}}^{2}\right)}{5.00\times {\text{10}}^{5}\text{kg}}=\text{6.20}{\text{m/s}}^{2}\\[/latex]

3. Use Newton’s laws of motion.

Two forces are acting on an object of mass m: F, shown by an arrow pointing upward, and its weight w, shown by an arrow pointing downward. Acceleration a is represented by a vector arrow pointing upward. The figure depicts the forces acting on a high jumper.

[latex]F=\left(\text{70.0 kg}\right)\left[\left(\text{39}\text{.}{\text{2 m/s}}^{2}\right)+\left(9\text{.}{\text{80 m/s}}^{2}\right)\right]\\[/latex] [latex]=3.\text{43}\times {\text{10}}^{3}\text{N}\\[/latex].  The force exerted by the high-jumper is actually down on the ground, but F is up from the ground and makes him jump.

  • This result is reasonable, since it is quite possible for a person to exert a force of the magnitude of 10 3 N.

5. (a) 4.41 × 10 5 N (b) 1.50 × 10 5 N

7. (a) 910 N (b) 1.11 × 10 3

9. (a) a = 0.139 m/s, θ = 12.4º

11. Use Newton’s laws since we are looking for forces.

  • Draw a free-body diagram:

A horizontal dotted line with two vectors extending downward from the mid-point of the dotted line, both at angles of fifteen degrees. A third vector points straight downward from the intersection of the first two angles, bisecting them; it is perpendicular to the dotted line.

  • The tension is given as T = 25.0 N. Find F app . Using Newton’s laws gives:[latex]\sigma{F}_{y}=0\\[/latex], so that applied force is due to the y -components of the two tensions: F app = 2 T  sin  θ  = 2(25.0 N) sin(15º) = 12.9 N The x -components of the tension cancel. [latex]\sum{F}_{x}=0\\[/latex].
  • This seems reasonable, since the applied tensions should be greater than the force applied to the tooth.
  • College Physics. Authored by : OpenStax College. Located at : http://cnx.org/contents/031da8d3-b525-429c-80cf-6c8ed997733a/College_Physics . License : CC BY: Attribution . License Terms : Located at License

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what is problem solving in physics

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Physics is a branch of science that studies the properties of matter, energy, and many more. Physics is considered to be the most fundamental of all the sciences, and is also the oldest.

  • 2 History of Physics
  • 3.1 Isaac Newton
  • 3.2 Albert Einstein
  • 4 Classical Mechanics
  • 5 Statistical Mechanics
  • 6 Acoustics
  • 8 Thermodynamics
  • 9 Electromagnetism
  • 10 See also

Physics before the 19th century is called Classical Physics . Physics after the 19th century is know as Modern Physics .

Classical Physics can be split even further into its own branches:

  • Classical Mechanics
  • Statistical Mechanics
  • Thermodynamics
  • Electromagnetism

Modern Physics is also a group of different subjects in physics:

  • Quantum Mechanics
  • Nuclear Physics
  • Condensed Matter Physics
  • Particle Physics
  • Astrophysics

History of Physics

The history of physics is long and exciting. Physics started with the first scientist, Thales of Miletus, who was the first to try to systematically explain the world using theories and hypotheses instead of using gods and magic. Archimedes also made a big breakthrough in physics when he devised the concept of buoyancy . This discovery was in the third century BC and not much innovation was made thereafter for many centuries.

However, Galileo Galilei, an Italian scientist, first advocated for the systematic study of physics. He was the one who tried to preach his scientific thoughts about how the Earth orbited the Sun, opposing the ideas of the Catholic establishment, and became the first patron of physics.

This was then further developed by Sir Isaac Newton , an English scientist, who devised the modern study of physics by discovering many laws. Since then, physics has never looked back!

Notable Figures

Isaac newton.

Isaac Newton was born on January 4, 1643, in Lincolnshire, England. Newton was born very shortly after the death of his father. He did very well at his local school and later attended Trinity College.

What is now considered Newton's most famous achievement is the formal statement of three basic, almost trivial laws of motion:

  • If the net force on any amount of matter is Zero , then the object's velocity will not change if viewing from a constant reference point.

$m$

Albert Einstein

$E=MC^{2}$

Relativity is a branch of modern science that has two parts: special relativity and general relativity. Both were formed by Albert Einstein.

Mechanics is the study of movement. Kinematics , mechanical forces , work , power , energy , and matter are all part of mechanics.

$\delta x'(t)=v(t)$

The rules of physics are almost fully summarized by the three famous laws of motion formulated by Isaac Newton :

  • A body continues to be in its state of uniform rectilinear motion until it is disturbed by an external force. This property is known as inertia.
  • The rate of change of momentum of a body with respect to time is directly proportional to the force acting on it.
  • Every action has an equal and opposite reaction.

Mass is one of the two most basic intrinsic properties of a body. It is a measure of its inertia . Momentum is defined as the product of the mass and velocity of a body. Force is something that changes or tends to change the momentum of a body, (informally, a "push or pull").

$W =\int^{x_f}_{x_i} F\,dx$

Among the various properties of matter are elasticity, surface tension, and viscosity. The most important one is gravity . Gravity is indeed considered one of the most mysterious things not only in physics but in science as a whole.

Newton's laws can also be used to study the behavior of continuous substances. This has, for example, led to the development of fluid mechanics , which, despite being almost entirely summarized by the Navier-Stokes equations or its variants, has many open questions about, for example, whether fluids continue to be well-behaved after arbitrary amounts of time.

Statistical Mechanics is mechanics that use statistics to draw conclusions.

Acoustics is the study of sound . Sound waves are mechanical waves - they travel by actual vibrations in some material medium. Acoustics concerns itself with mechanical waves in general. Phenomena such as forced vibrations , resonance , damped vibrations and the Doppler effect come under this branch of physics.

Optics is the study of vision and light. Light waves are electromagnetic waves - they consist of mutually perpendicular electric fields and magnetic fields , and can travel through a vacuum. Optics is the study of electromagnetic waves in general. So it covers all waves in the electromagnetic spectrum given below:

  • Ultraviolet rays
  • Visible light
  • Infrared Rays
  • Radio waves

One of the most controversial questions in optics is whether light is a wave or a ray. Accordingly, there are two branches of optics, but only ray optics belongs to classical physics. Wave optics are a topic of modern physics. In ray, optics covers topics such as reflection and refraction and the dispersion of white light into its constituent colors.

Thermodynamics is the study of heat transfer. Anything in physics related to heat is classified as thermodynamics. There are three laws of thermodynamics:

  • The First Law of Thermodynamics is a form of conservation of energy: The change in internal energy of a system is equal to the sum of the energy transferred to the system by heat and the work done on the system.
  • The Second Law of Thermodynamics states that the efficiency of heat engines must always be < 1.
  • The Third Law of Thermodynamics states that the temperature of a system cannot reach absolute zero (0 K); as the system approaches absolute zero, entropy approaches a constant.

Electromagnetism is the combined study of electricity and magnetism , and the most important addition to classical physics after Isaac Newton 's work. The concept of electromagnetism has wide applications in everyday devices such as modern computers, televisions, linear particle accelerators, and more. Electromagnetism operates on the fact that when electricity is run through a conductor, it produces a magnetic field

  • Physics books
  • Physics competitions
  • Physics scholarships
  • Physics summer programs
  • Electricity

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what is problem solving in physics

PHYSICS PROBLEM SOLVING STRATEGY Dr. Mark Hollabaugh Normandale Community College

http://www.nr.cc.mn.us/physics/Faculty/HOLLABGH/probsolv.htm

    Two factors can help make you a better physics problem solver.  First of all, you must know and understand the principles of physics.  Secondly, you must have a strategy for applying these principles to new situations in which physics can be helpful.  We call these situations problems.  Many students say, “I understand the material, I just can’t do the problems.”  If this is true of you as a physics student, then maybe you need to develop your problem-solving skills.  Having a strategy to organize those skills can help you.

    Physics problem solving can be learned just like you learned to drive a car, play a musical instrument, or ride a bike.  What can aid you more than anything is to have a general approach to follow with each problem you encounter.  You may use different tools or tactics with differing areas of physics, but the overall strategy remains the same.  Most likely, you have already acquired some problem-solving skills and habits from previous courses in physics, chemistry, or mathematics.  Like other areas of learning and life, some of these habits may be beneficial and some may actually hinder your progress in learning how to solve physics problems.

    So, in learning this new approach, be willing to try new ideas and to discard old habits that may in fact be hindering your understanding.  As you mature as a physics problem solver, you will find that the approach will become second nature to you.  You will begin automatically to do those things that will lead you to construct an effective solution to the problem.

    As with so many other learning activities, it is useful to break a problem solving strategy into major and minor steps.  The strategy we would like you to learn has five major steps:  Focus the Problem , Physics Description , Plan a Solution , Execute the Plan , and Evaluate the Solution .  Let’s take a detailed look at each of these steps and then do an sample problem following the strategy.  At this stage of our discussion, do not worry if there are physics terms or concepts that you do not understand.  You will learn these concepts as they are needed.  Then, refer back to this discussion.

FOCUS the PROBLEM      Usually when you read the statement of a physics problem, you must visualize the objects involved and their context.  You need to draw a picture and indicate any given information.

(1) First, construct a mental image of the problem situation. (2)Next draw a rough, although literal, picture showing the important objects, their motion, and their interactions.  An interaction, for example, may consist of one object being connected to another by a rope. (3) Label all known information.  At this point, do not worry about assigning algebraic symbols to specific quantities.

    Sometimes the question being asked in the problem is not obvious.  “Is the rope safe?” is not something you can directly answer.  Ask yourself, what specifically is being asked?  How does this translate into some calculable quantity?

    There are many ways to solve a physics problem.  One part of learning how to solve a problem is to know what approach to use.  You will need to outline the concepts and principles you think will be useful in solving the problem.

If simple motions are involved, use the kinematics definition of velocity and acceleration. If forces are involved and objects interact due to these forces, use Newton's Laws of Motion. Forces that act over a time interval and cause objects to change their velocities suggests using the Conservation of Momentum. Frequently in situations involving thermal physics or electromagnetism, the principle of Conservation of Energy is useful. You may need to specify time intervals over which the application of each principle will be the most useful. It is important to identify any constraints present in this situation, such as “the car doesn’t leave the road”. Specify any approximations or simplifications you think will make the problem solution easier, but will not affect the result significantly.  Frequently we ignore frictional forces due to air resistance.

    Your approach probably will be very consistent throughout a particular section of the textbook.  The challenge for you will be to apply the approach in a variety of situations.

DESCRIBE the PHYSICS      A “physics description” of a problem translates  the given information and a very literal picture into an idealized diagram and defines variables that can be manipulated to calculate desired quantities.  In a sense, you are translating the literal situation into an idealized situation where you can then apply the laws the physics.  The biggest shortcoming of beginning physics problem solvers is attempting to apply the laws of physics, that is write down equations, before undertaking this qualitative analysis of the problem.  If you can resist the temptation to look for equations too early in your problem solution, you will become a much more effective problem solver.

To construct your physics description, you must do the following:

  • Translate your picture into a diagram(s) which gives only the essential information for a mathematical solution.  In an idealized diagram, people, cars, and other objects may become square blocks or points.
  • Define a symbol for every important physics variable on your diagram.
  • Usually you need to draw a coordinate system showing the + and - directions.
  • If you are using kinematics concepts, draw a motion diagram specifying the objects’ velocity and acceleration at definite positions and times.
  • If interactions are important, draw idealized, free body, and force diagrams.
  • When using conservation principles, draw "before", "transfer" (i.e., during), and "after" diagrams to show how the system changes. To the side of your diagram(s), give the value for each physics variable you have labeled on the diagram(s) or specify that it is unknown.

    Then, using the question, your physics description and the approach you have stated, you will need to identify a target variable.  That is, you must decide what unknown quantity is it that you must calculate from your list of variables.  Ask yourself if the calculated quantity answers the question.  In complex problems there may be more than one target variable or some intermediate variables you will calculate.

     Now, knowing the target variable(s), and your approach, you can assemble your toolbox of mathematical expressions using the principles and constraints from your approach to relate the physics variables from your diagrams.  This is the first time you really begin to look for quantitative relationships among the variables.

 PLAN the SOLUTION     Before you actually begin to calculate an answer, take time to make a plan.  Usually when the laws of physics are expressed in an equation, the equation is a general, universal statement.  You must construct specific algebraic equations that will enable you to calculate the target variable.

  • Determine how the equations in your toolbox can be combined to find your target variable. Begin with an equation containing the target variable.
  • Identify any unknowns in that equation.
  • Find equations from your toolbox containing these unknowns.
  • Continue this process until your equations contain no new unknowns.
  • Number each equation for easy reference.
  • Do not solve equations numerically at this time.

    Frequently expert problem solvers will start with the target variable and work backwards to determine a path to the answer.  Sometimes the units will help you find the correct path.  For example, if you are looking for a velocity, you know your final answer must be in m/s.

    You have a solution if your plan has as many independent equations as there are unknowns.  If not, determine other equations or check the plan to see if it is likely that a variable will cancel from your equations.

    If you have the same number of equations and unknowns, indicate the order in which to solve the equations algebraically for the target variable. Typically, you begin your construction of the plan at the end and work backwards to the first step,  That is, you write down the equation containing the target variable first.

EXECUTE the PLAN     Now you are ready to execute the plan.

  • Do the algebra in the order given by your outline.
  • When you are done you should have a single equation with your target variable isolated on one side and only known quantities on the other side.
  • Substitute the values (numbers with units) into this final equation.
  • Make sure units are consistent so that they will cancel properly.

    Finally, calculate the numerical result for the target variable(s).  Make sure your final answer is clear to the person who will evaluate your solution.

    It is extremely important to solve the problem algebraically before inserting any numerical values.  Some unknown quantities may cancel out and you won’t need to actually know their numerical value.  In some complex problems it can be useful to calculate intermediate numerical results as a check on the reasonableness of your solution.

EVALUATE the SOLUTION      Finally, you are ready to evaluate your answer.  Here, you must use your common sense about how the real world works as well as those aspects of the physical world you have learned in your physics class.

  • Do vector quantities have both magnitude and direction?
  • Can someone else follow your solution?
  • Is the result reasonable and within your experience?  Remember, for example, that cars don’t travel down the highway at 300 mi/hr.  If you put a cooler object into hot water, the water cools down and the object rises in temperature.
  • Do the units make sense?  Velocity is not measured, for example, in kg/s.
  • Have you answered the question?

    Whenever possible, it is a good idea to read through the solution carefully, especially if it is being evaluated by your instructor.  If your evaluation suggests to you that your answer is incorrect or unreasonable, make a statement to that effect and explain your reasoning.  

Further Reading:

Patricia Heller, Ronald Keith, and Scott Anderson (1992), Teaching Problem Solving Through Cooperative Grouping.  Part 1:  Group Versus Individual Problem Solving, American Journal of Physics , Vol. 60, No. 7, pp. 627-636.

Patricia Heller and Mark Hollabaugh (1992), Teaching Problem Solving Through Cooperative Grouping.  Part 2:  Designing Problems and Structuring Groups,  American Journal of Physics , Vol. 60, No. 7, pp. 637-644.  

Physics Problems with Solutions

Projectile problems with solutions and explanations, problems with detailed solutions.

An object is launched at a velocity of 20 m/s in a direction making an angle of 25° upward with the horizontal. a) What is the maximum height reached by the object? b) What is the total flight time (between launch and touching the ground) of the object? c) What is the horizontal range (maximum x above ground) of the object? d) What is the magnitude of the velocity of the object just before it hits the ground? Solution to Problem 1

A ball kicked from ground level at an initial velocity of 60 m/s and an angle θ with ground reaches a horizontal distance of 200 meters. a) What is the size of angle θ? b) What is time of flight of the ball? Solution to Problem 5

A ball of 600 grams is kicked at an angle of 35° with the ground with an initial velocity V 0 . a) What is the initial velocity V 0 of the ball if its kinetic energy is 22 Joules when its height is maximum? b) What is the maximum height reached by the ball Solution to Problem 6

A projectile starting from ground hits a target on the ground located at a distance of 1000 meters after 40 seconds. a) What is the size of the angle θ? b) At what initial velocity was the projectile launched? Solution to Problem 7

The trajectory of a projectile launched from ground is given by the equation y = -0.025 x 2 + 0.5 x, where x and y are the coordinate of the projectile on a rectangular system of axes. a) Find the initial velocity and the angle at which the projectile is launched. Solution to Problem 8

Two balls A and B of masses 100 grams and 300 grams respectively are pushed horizontally from a table of height 3 meters. Ball has is pushed so that its initial velocity is 10 m/s and ball B is pushed so that its initial velocity is 15 m/s. a) Find the time it takes each ball to hit the ground. b) What is the difference in the distance between the points of impact of the two balls on the ground? Solution to Problem 9

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