AP Physics 1 Unit 3 Review: Work, Energy, and Power

Q: What's on the AP Physics 1 Unit 3 progress check (MCQ and FRQ)?

The AP Physics 1 Unit 3 progress check in AP Classroom includes both MCQ and FRQ parts drawn from all 5 unit topics: Translational Kinetic Energy, Work, Potential Energy, Conservation of Energy, and Power. The MCQ section tests conceptual understanding and calculation across these topics, while the FRQ section asks you to analyze scenarios using energy representations like bar charts and equations. For matched practice on every progress check topic, visit AP Physics 1 Unit 3 .

Q: How do I practice AP Physics 1 Unit 3 FRQs?

AP Physics 1 Unit 3 FRQs most often focus on conservation of energy and work, asking you to set up energy equations, draw or interpret bar charts, and justify your reasoning in writing. Practice by working through scenarios where a force does work on an object and tracking how kinetic and potential energy change. Write out full explanations, not just numbers. College Board released FRQs are the best benchmark. You can also find targeted FRQ practice at AP Physics 1 Unit 3 .

Q: Where can I find AP Physics 1 Unit 3 practice questions?

For AP Physics 1 Unit 3 practice questions, including MCQ and practice test sets, head to AP Physics 1 Unit 3 . You'll find questions covering work, energy, conservation of energy, and power that mirror the style of the actual AP exam. For the best results, mix multiple-choice practice with full FRQ attempts so you're ready for both question formats on test day.

Q: How should I study AP Physics 1 Unit 3?

Start with work as the core concept, since it connects force and displacement to every other idea in the unit. Build up through translational kinetic energy and potential energy before tackling conservation of energy, which is the most tested topic at 18-23% of the exam. Use energy bar charts to visualize how energy transfers between forms. Then practice power problems, which are often calculation-heavy. After each topic, do a short set of MCQs to check your understanding before moving on. AP Physics 1 Unit 3 has study guides and practice organized by topic to keep you on track.

18–23% of AP multiple choice
5 topics
AP exam review verified for 2027

Unit 3 is about how energy is stored, transferred, and conserved in physical systems. Work is the mechanism that changes a system's energy, potential energy is stored energy tied to position within a system, and conservation of energy lets you relate initial and final states without solving for every intermediate step.

Fiveable's AP Physics 1 Unit 3 review covers 5 topics, with guided practice questions for the unit.

start with 3.1 start unit practiceReview with a tutorFree, 24/7, real people, from UPchieve

AP Physics 1 unit 3 topics

3.1

Translational Kinetic Energy

Define kinetic energy using K = 1/2 mv^2, recognize it as a scalar that depends on speed squared, and explain why different observers in different reference frames measure different values of K for the same object.

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3.2

Work

Calculate work using W = Fd cos theta, apply the work-energy theorem Delta K = net W, distinguish conservative from nonconservative forces, and read work from force-displacement graphs.

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3.3

Potential Energy

Write expressions for gravitational PE (Delta U_g = mg Delta y) and elastic PE (U_s = 1/2 k Delta x^2), explain why only changes in PE matter, and connect PE to the object-Earth or object-spring system.

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3.4

Conservation of Energy

Apply K_i + U_i = K_f + U_f for conservative systems, account for energy dissipated by friction using W_nc = Delta E_mech, and justify whether mechanical energy is conserved based on system boundary and force types.

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3.5

Power

Calculate average power with P_avg = Delta E / Delta t and instantaneous power with P_inst = Fv cos theta, use watts as the SI unit, and interpret the sign of power as the direction of energy transfer.

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Practice AP Physics 1 unit 3 questions

Try AP-style questions on unit 3, then use the review notes below for anything you miss.

Example stimulus-based MCQs

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setup_diagram

Stimulus-based practice question

A sled of mass $20 \text{ kg}$ is pulled across a rough horizontal surface at a constant speed by a rope angled at $60^\circ$ above the horizontal, as shown in the figure. The tension in the rope is $50 \text{ N}$ .

answer in practice

Question

Which of the following is most nearly the work done by friction on the sled as it moves a horizontal distance of $10 \text{ m}$ ?

$-500 \text{ J}$

$-433 \text{ J}$

$-250 \text{ J}$

$0 \text{ J}$

setup_diagram

Stimulus-based practice question

A block of mass $m$ slides to the right with initial speed $v_0$ across a rough horizontal surface with coefficient of kinetic friction $\mu_k$ , as shown in the figure.

answer in practice

Question

Which of the following correctly describes the change in total mechanical energy of the system defined as the block only, and why?

It decreases because friction is an internal force that converts mechanical energy to thermal energy within the system.

It remains constant because the work done by friction equals the work done by the applied force on the block.

It decreases because friction removes energy from the block and transfers it to the surroundings as heat.

It decreases because the external force of friction does negative work on the block.

Example FRQs

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FRQ

Work-energy principle, net forces, final velocity

4. In Scenario 1, a student pushes a cart of mass $m = 2.0\ \text{kg}$ up a straight incline that makes an angle $\theta = 30^\circ$ above the horizontal, as shown in Figure 1. The cart starts from rest and moves a distance $d = 4.0\ \text{m}$ along the incline while the student applies a constant force of magnitude $F_1 = 18\ \text{N}$ parallel to the incline. The coefficient of kinetic friction between the cart and the incline is $\mu_k = 0.20$ . The cart remains in contact with the incline.

In Scenario 2, the student repeats the experiment on the same incline with the same cart and the same friction conditions, but applies a different constant force of magnitude $F_2 = 22\ \text{N}$ parallel to the incline. The cart again starts from rest and moves the same distance $d = 4.0\ \text{m}$ along the incline.

Figure 1. Cart pushed up a 30° incline; displacement along the incline is 4.0 m. Forces on the cart are shown: applied force parallel up the incline, kinetic friction parallel down the incline, weight vertically downward, and normal force perpendicular to the incline.

Refer to Figure 1. Indicate whether $v_1$ is greater than, less than, or equal to $v_2$ by writing one of the following in your answer booklet.

• $v_1 > v_2$
• $v_1 < v_2$
• $v_1 = v_2$

Justify your answer in terms of the work done by ALL forces acting on the cart over the distance $d$ in each scenario. Use qualitative reasoning beyond referencing equations.

Starting with the work-energy principle, derive an expression for the cart's final speed $v$ after it moves the distance $d$ . Express your answer in terms of $F$ , $m$ , $d$ , $\theta$ , $\mu_k$ , and physical constants, as appropriate. Begin your derivation by writing a fundamental physics principle or an equation from the reference information. Consider the general case of a cart of mass $m = 2.0\ \text{kg}$ moving up the same incline of angle $\theta = 30^\circ$ a distance $d = 4.0\ \text{m}$ while a constant applied force $F$ acts parallel to the incline. The coefficient of kinetic friction is $\mu_k = 0.20$ . The cart starts from rest.

Indicate whether the expression for $v$ you derived in part B is or is not consistent with the claim made in part A. Briefly justify your answer by referencing your derivation in part B.

write this FRQ more Qualitative/Quantitative FRQs in this unit

FRQ

Block energy conversion and system work analysis

1. A block of mass 2.0 kg is released from rest at the top of a ramp and slides down, then moves onto a horizontal surface and compresses a spring, as shown in Figure 1. The spring is located at the bottom of the ramp, so the block first contacts the spring at the instant it reaches the bottom of the ramp.

Figure 1. Block sliding down a 30° ramp with kinetic friction, then compressing a spring on a frictionless horizontal surface.

Figure 2. Blank axes for graphing kinetic energy K versus spring compression x from first contact to maximum compression.

On the axes shown in Figure 2, sketch a graph of the kinetic energy $K$ of the block as a function of the spring compression $x$ from $x = 0$ (first contact) to $x = x_{\max}$ (maximum compression).

ii.

Derive an expression for the speed $v_1$ of the block at the instant it first contacts the spring (at $t=t_1$ ) in terms of $m$ , $g$ , $h$ , $\mu_k$ , $\theta$ , and any other given quantities, as appropriate. Begin your derivation by writing a fundamental physics principle or an equation from the reference information.

iii.

Derive an expression for the maximum compression $x_{\max}$ of the spring (at $t=t_2$ ) in terms of $m$ , $g$ , $h$ , $\mu_k$ , $\theta$ , $k$ , and any other given quantities, as appropriate. Begin your derivation by writing a fundamental physics principle or an equation from the reference information.

Indicate whether the student’s claim is correct. A student claims that mechanical energy is conserved for the system consisting of the block and Earth during the entire motion from $t=0$ to $t=t_2$ .

During the motion, the block experiences kinetic friction on the ramp (coefficient $\mu_k = 0.20$ ), and the horizontal surface is frictionless. The spring has spring constant $k = 400\ \text{N/m}$ .

Correct
Incorrect
Justify your response by explicitly identifying (1) the system you are considering and (2) whether energy is transferred into or out of that system by an external force.

write this FRQ more Mathematical Routines FRQs in this unit

FRQ

Spring constant determination through experimental data collection

3. Students are investigating the relationship between elastic potential energy and kinetic energy using the following setup.

Describe an experimental procedure to collect data that would allow the students to determine the spring constant k. Include any steps necessary to reduce experimental uncertainty.

Describe how the data collected in part A could be graphed and how that graph would be analyzed to determine k.

Figure 1. Spring-block setup on horizontal track

Figure 2. Blank graph grid for linearized relationship

x (m)	v (m/s)
0.10	1.8
0.15	2.7
0.20	3.5
0.25	4.6
0.30	5.3
0.35	6.2

The students conduct the experiment described in part A. Table 1 shows the compression distance x and the corresponding speed v of the block as it leaves the spring.

The students correctly determine that the relationship between v and x is given by v² = (k/m)x².

The students create a graph with x² plotted on the horizontal axis.

Indicate what measured or calculated quantity could be plotted on the vertical axis to yield a linear graph whose slope can be used to calculate an experimental value for the spring constant k.

Vertical axis: Horizontal axis: x² (m²)

ii.

On the grid in Figure 2, create a graph of the quantities indicated in part C(i) that can be used to determine k.

•

Use Table 2 to record the data points or calculated quantities that you will plot.

•

Clearly label the vertical axis, including units as appropriate.

•

Plot the points you recorded in Table 2.

iii.

Draw a straight best-fit line for the data graphed in part C(ii).

Figure 3. Spring-block system on an incline

Using the best-fit line that you drew in part C(iii), calculate the magnitude of the work done by friction on the block as it travels the distance d up the incline. The students conduct a second experiment using the setup shown in Figure 3. A block of mass M = 0.80 kg is pressed against the same spring, compressing it a distance x₀ = 0.25 m. The spring-block system is on an inclined track that makes an angle θ = 15° with the horizontal. The block is released from rest and travels up the incline a distance d = 1.2 m before momentarily stopping. Friction between the block and the inclined track is not negligible.

write this FRQ more Experimental Design FRQs in this unit

AP Physics 1 unit 3 practice test

A timed, AP-style test built only from unit 3 questions — multiple choice plus free response, scored with AI feedback. Use the standard format or build your own.

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Unit 3 review notes

3.1

Translational Kinetic Energy

Translational kinetic energy is the energy an object has due to its translational motion. It depends on both mass and speed, but speed is squared, so doubling speed quadruples kinetic energy while doubling mass only doubles it. Because kinetic energy is a scalar, it is always zero or positive and has no directional component.

Formula: K = 1/2 mv^2, where m is mass in kg and v is speed in m/s; result is in joules.
Scalar quantity: Kinetic energy has magnitude only. Two objects moving in opposite directions at the same speed have the same kinetic energy.
Frame-of-reference dependence: Different observers in different inertial frames measure different speeds for the same object and therefore calculate different values of K. There is no single correct value independent of frame.
Speed vs velocity: K depends on the magnitude of velocity (speed), not its direction, so only the speed term v enters the formula.

A 2 kg cart moves at 3 m/s. What is its kinetic energy? If the cart's speed doubles to 6 m/s, by what factor does K change?

Quantity	Doubles mass (2m)	Doubles speed (2v)
Effect on K	K doubles	K quadruples
New K expression	2 * (1/2 mv^2)	1/2 m(2v)^2 = 4 * (1/2 mv^2)

3.2

Work

Work is the scalar measure of energy transferred into or out of a system by a force acting over a displacement. Only the component of force parallel to the displacement contributes. Work can be positive (force and displacement in the same direction), negative (force opposes displacement), or zero (force perpendicular to displacement, as with normal force on horizontal motion). The work-energy theorem states that the net work done on an object equals its change in kinetic energy.

W = Fd cos theta: Work equals force magnitude times displacement magnitude times the cosine of the angle between them. Units are joules.
Work-energy theorem: Delta K = sum of all work done on the object. Net positive work increases kinetic energy; net negative work decreases it.
Conservative force: A force whose work is path-independent and depends only on initial and final positions. Gravity and ideal springs are conservative. Work done over a closed path is zero.
Nonconservative force: A force whose work depends on the path taken. Kinetic friction and air resistance are nonconservative; they convert mechanical energy to thermal energy.
Force-displacement graph: For a variable force, the work done equals the area under the F-parallel vs displacement curve.

A 10 N force is applied at 60 degrees to the horizontal as a box moves 4 m horizontally. How much work does the force do? Is this positive or negative work?

Force type	Path dependence	Example	Potential energy?
Conservative	Path-independent	Gravity, ideal spring	Yes
Nonconservative	Path-dependent	Kinetic friction, air resistance	No

3.3

Potential Energy

Potential energy is stored energy that belongs to a system of two or more objects interacting through conservative forces. It is a scalar associated with the configuration (positions) of objects within the system, not with any single object alone. The choice of zero potential energy is arbitrary and set by the observer to simplify analysis; only changes in potential energy are physically meaningful.

Gravitational PE near Earth: Delta U_g = mg Delta y, where y is measured upward from the chosen reference level. The object-Earth system stores this energy.
Elastic PE of a spring: U_s = 1/2 k(Delta x)^2, where k is the spring constant and Delta x is the stretch or compression from equilibrium. Always positive or zero.
Zero PE reference: You choose where U = 0. Setting the reference at the lowest point of a problem often simplifies algebra, but the physics is the same regardless of choice.
Object-Earth system: Gravitational potential energy is a property of the object-Earth system, not of the object alone. This framing is important for system-boundary reasoning.
Conservative forces only: Potential energy can only be defined for conservative forces. There is no potential energy associated with friction or air resistance.

A spring with k = 200 N/m is compressed 0.15 m. What is the elastic potential energy stored in the spring-object system?

Type	Formula	System	Depends on
Gravitational (near Earth)	Delta U_g = mg Delta y	Object-Earth	Height change
Elastic (ideal spring)	U_s = 1/2 k(Delta x)^2	Object-spring	Compression or stretch from equilibrium

3.4

Conservation of Energy

Mechanical energy is the sum of a system's kinetic and potential energies: E_mech = K + U. If only conservative forces act within a system and no work crosses the system boundary, E_mech is constant. When nonconservative forces like friction act inside the system, mechanical energy decreases by the magnitude of work done by those forces, and that energy appears as thermal energy or sound. Defining the system boundary determines whether energy is conserved or transferred.

Mechanical energy: E_mech = K + U. Includes all kinetic and potential energies of objects within the system.
Conservation condition: If net work by nonconservative forces is zero and no energy crosses the boundary, Delta E_mech = 0, so K_i + U_i = K_f + U_f.
Nonconservative work: W_nc = Delta E_mech. Friction does negative work on the system, reducing mechanical energy by converting it to thermal energy.
System boundary selection: Expanding the system to include the surface and object together means friction becomes an internal interaction; total energy including thermal energy is still conserved.
Energy dissipation: Kinetic friction converts mechanical energy to thermal energy. This energy is not lost from the universe but is no longer available as mechanical energy.

A 0.5 kg ball is released from rest at a height of 2 m above the ground. Using conservation of energy and ignoring air resistance, what is its speed just before it hits the ground?

System type	Nonconservative forces inside?	E_mech behavior	Equation form
Isolated, conservative only	No	Constant	K_i + U_i = K_f + U_f
With friction or drag	Yes	Decreases	K_i + U_i + W_nc = K_f + U_f

3.5

Power

Power is the rate at which energy is transferred or converted. Average power equals total energy change divided by elapsed time. Instantaneous power delivered by a constant force equals the component of that force parallel to the object's velocity multiplied by the speed. The SI unit of power is the watt, equal to one joule per second.

Average power: P_avg = Delta E / Delta t = W / Delta t. Use this when you know total energy change and total time.
Instantaneous power: P_inst = F_parallel * v = Fv cos theta. Use this when you know force and speed at a specific moment.
Watt: The SI unit of power: 1 W = 1 J/s. Power can be positive (energy into system) or negative (energy out of system).
Sign of power: Positive power means energy is being transferred into the system or object; negative power means energy is being removed.

A motor lifts a 50 kg crate 8 m in 10 seconds at constant speed. What is the average power output of the motor?

Formula	When to use	Variables needed
P_avg = Delta E / Delta t	Total energy change over a time interval	Energy change, time
P_avg = W / Delta t	Work done over a time interval	Work, time
P_inst = Fv cos theta	Force and speed at one instant	Force magnitude, speed, angle

Key terms

Term	Definition
object-Earth system	A system consisting of an object and Earth, used to analyze gravitational potential energy and mechanical energy transformations.
scalar	A physical quantity described by magnitude only, without direction. Kinetic energy, potential energy, work, and power are all scalars.

How to review unit 3

Topics students miss most

Miss rates come from Fiveable multiple-choice practice.

3.5

Power

43%1,051 tries

3.3

Potential Energy

42%1,306 tries

3.2

Work

36%1,388 tries

Common unit 3 mistakes

Treating kinetic energy as a vector

K is a scalar. Two objects moving in opposite directions at the same speed have identical kinetic energies. Do not assign direction to K or add kinetic energies using vector rules.

Using the wrong angle in W = Fd cos theta

The angle theta is between the force vector and the displacement vector, not between the force and the horizontal. Sketch both vectors and measure the angle between them before substituting.

Assigning potential energy to a single object

Gravitational and elastic potential energy belong to a system of interacting objects, such as the object-Earth system. Saying a ball has gravitational PE on its own is imprecise and can cause errors in system-boundary problems.

Applying conservation of mechanical energy when friction is present

If kinetic friction or air resistance acts inside the system, mechanical energy is not conserved. You must include the work done by nonconservative forces: W_nc = Delta E_mech.

Confusing average power with instantaneous power

P_avg = W / Delta t gives the average rate over a time interval. P_inst = Fv cos theta gives the rate at one specific moment. Using the wrong formula, especially when force or speed is changing, produces incorrect results.

How this unit shows up on the AP exam

Quantitative energy tracking across a scenario

Exam questions frequently present a multi-stage scenario, such as a block released from a compressed spring, sliding along a surface with friction, and rising up a ramp. You are expected to write energy equations at each transition, account for work done by friction, and solve for an unknown speed or height. Showing explicit system definitions and labeling each energy term is rewarded in free-response scoring.

Qualitative and graphical reasoning about energy

Questions may show a force-displacement graph and ask for work as the area under the curve, or show an energy-position graph and ask you to identify where kinetic energy is maximum or where the object momentarily stops. Being able to translate between graphical representations and energy equations is a tested skill throughout Unit 3.

Justifying system and boundary choices in written responses

Free-response tasks often ask you to explain why mechanical energy is or is not conserved for a given scenario. A complete response names the system, identifies whether nonconservative forces act within it, and connects that identification to the conclusion about energy conservation. Vague answers that omit system definition or force type typically receive partial credit only.

More ways to review

Topic study guides

Open the individual guides for Unit 3 when you want a closer review of one topic.

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Practice questions

Use AP-style practice after you review the notes so you can check what you understand.

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FRQ practice

Practice free-response reasoning and compare your answer with scoring guidance.

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Cram archive videos

Watch past review streams filtered to Unit 3 when you want a video walkthrough.

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Official unit cheatsheet

Open the Fiveable one-page unit review, then explore visual cheatsheets for a quick refresher.

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Score calculator

Estimate your broader AP score goal after you review the course and exam format.

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Unit 3 printables

Print the unit cheatsheets ($3) for Unit 3. Yours to keep, no subscription needed.

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Frequently Asked Questions

What's on the AP Physics 1 Unit 3 progress check (MCQ and FRQ)?

The AP Physics 1 Unit 3 progress check in AP Classroom includes both MCQ and FRQ parts drawn from all 5 unit topics: Translational Kinetic Energy, Work, Potential Energy, Conservation of Energy, and Power. The MCQ section tests conceptual understanding and calculation across these topics, while the FRQ section asks you to analyze scenarios using energy representations like bar charts and equations. For matched practice on every progress check topic, visit AP Physics 1 Unit 3.

How do I practice AP Physics 1 Unit 3 FRQs?

AP Physics 1 Unit 3 FRQs most often focus on conservation of energy and work, asking you to set up energy equations, draw or interpret bar charts, and justify your reasoning in writing. Practice by working through scenarios where a force does work on an object and tracking how kinetic and potential energy change. Write out full explanations, not just numbers. College Board released FRQs are the best benchmark. You can also find targeted FRQ practice at AP Physics 1 Unit 3.

Where can I find AP Physics 1 Unit 3 practice questions?

For AP Physics 1 Unit 3 practice questions, including MCQ and practice test sets, head to AP Physics 1 Unit 3. You'll find questions covering work, energy, conservation of energy, and power that mirror the style of the actual AP exam. For the best results, mix multiple-choice practice with full FRQ attempts so you're ready for both question formats on test day.

How should I study AP Physics 1 Unit 3?

Start with work as the core concept, since it connects force and displacement to every other idea in the unit. Build up through translational kinetic energy and potential energy before tackling conservation of energy, which is the most tested topic at 18-23% of the exam. Use energy bar charts to visualize how energy transfers between forms. Then practice power problems, which are often calculation-heavy. After each topic, do a short set of MCQs to check your understanding before moving on. AP Physics 1 Unit 3 has study guides and practice organized by topic to keep you on track.

Ready to review Unit 3?Start with the notes, check the topic cards, and use the practice or resource links when they are available for this course.

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