Work Energy and Power — Free AP Physics 1 Review Games.
This unit covers work-energy theorem, kinetic energy, potential energy and conservation of energy — essential concepts for AP Physics 1. Use our interactive study games to test your understanding, or review questions in traditional format below.
Pick a mode. Play.
Answer questions as fast as you can. 2 minutes on the clock. Build streaks for bonus points!
Don't want to play?
Review the questions traditionally. Click to expand.
Questions loading...
Focus on understanding.
Focus on understanding core concepts before memorizing details. Use the game modes to test yourself repeatedly — spaced repetition is proven to boost long-term retention.
Ready for college?
This unit covers work-energy theorem, kinetic energy, potential energy and conservation of energy — essential concepts for AP Physics 1. Use our interactive study games to test your understanding, or review questions in traditional format below.
Key Concepts Breakdown
1 Work-Energy Theorem
The net work done on an object equals the change in its kinetic energy: W_net = ΔKE. Work is done by a force only when there is displacement with a component parallel to the force. On the AP exam, you must apply this theorem to find speeds, forces, or displacements when multiple forces act on an object.
Key Points
- W = Fd cosθ, where θ is the angle between force and displacement vectors
- W_net = ΔKE = KE_f − KE_i
- Negative work means the force opposes motion and removes kinetic energy
- A force perpendicular to motion (e.g., normal force, centripetal force) does zero work
A 5 kg box initially moving at 4 m/s is pushed along a frictionless surface by a 20 N horizontal force over 10 m. What is the final speed?
Net work equals the applied force times displacement: W_net = 20 N × 10 m = 200 J. Using the work-energy theorem: 200 J = ½(5)(v²) − ½(5)(4²), which gives 200 = 2.5v² − 40, so v² = 96, v ≈ 9.8 m/s. The initial kinetic energy adds to the work input to yield the final kinetic energy.
2 Kinetic Energy
Kinetic energy is the energy of motion, defined as KE = ½mv². It is a scalar quantity that depends on mass linearly and on speed quadratically. The AP exam frequently tests how doubling speed quadruples KE, and how KE relates to net work and momentum.
Key Points
- KE = ½mv²; doubling speed quadruples KE, doubling mass only doubles KE
- KE is always non-negative; it is zero only when the object is at rest
- KE and momentum are related: KE = p²/(2m)
- Change in KE equals net work done on the object (work-energy theorem)
Car A (mass 1000 kg) moves at 20 m/s. Car B (mass 2000 kg) moves at 10 m/s. Which has greater kinetic energy?
KE_A = ½(1000)(20²) = 200,000 J. KE_B = ½(2000)(10²) = 100,000 J. Car A has twice the kinetic energy despite having half the mass, because the speed term is squared. This illustrates why speed has a stronger effect on KE than mass does.
3 Potential Energy
Potential energy is stored energy associated with an object's position in a force field. On the AP exam, gravitational PE (U_g = mgh) and elastic PE (U_s = ½kx²) are the two required forms. You must be able to identify the reference point for gravitational PE and use the spring constant to find elastic PE.
Key Points
- Gravitational PE: U_g = mgh, measured from a chosen reference height (h = 0 is your choice)
- Elastic PE: U_s = ½kx², where x is the compression or stretch from equilibrium
- PE is stored energy; it can be converted to KE and vice versa in a conservative system
- Only changes in PE are physically meaningful; the reference level cancels in energy conservation equations
A spring with k = 400 N/m is compressed 0.3 m and launches a 0.2 kg ball. What is the elastic PE stored in the spring?
Elastic PE = ½kx² = ½(400)(0.3²) = ½(400)(0.09) = 18 J. This 18 J of stored elastic PE will convert to kinetic energy of the ball upon release (assuming no friction or other losses). This type of calculation is a direct setup for an energy conservation problem that commonly appears on the AP exam.
4 Conservation of Energy
In a closed system with only conservative forces, total mechanical energy (KE + PE) is constant. When non-conservative forces like friction act, the work done by those forces equals the change in total mechanical energy: W_nc = ΔKE + ΔPE. This is the most heavily tested topic in this unit on the AP exam.
Key Points
- Without friction: KE_i + PE_i = KE_f + PE_f
- With friction or other non-conservative forces: W_nc = ΔE_mech = (KE_f + PE_f) − (KE_i + PE_i)
- Friction always removes mechanical energy (W_friction is negative); energy is dissipated as thermal energy
- At maximum height or when velocity = 0, KE = 0; at minimum height or equilibrium, PE is minimized and KE is maximized
A 2 kg block slides from rest down a 5 m frictionless ramp angled such that the bottom is 3 m below the start. What is the speed at the bottom?
Setting the bottom as the reference level (h = 0), initial energy is purely gravitational PE: E_i = mgh = 2(10)(3) = 60 J. At the bottom, all energy is kinetic: 60 J = ½(2)v², giving v² = 60, v ≈ 7.7 m/s. The ramp angle and length are irrelevant because only the vertical height drop determines the change in gravitational PE.
Questions, answered.
What is Work Energy and Power?
Work Energy and Power is Unit 3 of AP Physics 1, covering work-energy theorem, kinetic energy, potential energy and conservation of energy.
How to study for AP Physics 1 Unit 3?
Start with the Quick Summary above, review the Key Concepts, then test yourself with our interactive study games. Aim for 80%+ accuracy before moving on.
How many questions are in this unit?
This unit has 30+ review questions across 5 different game modes.