AP Physics 1 / Topic
Work, Energy, and Power
Unit 3 reframes mechanics in terms of energy: work done by forces, kinetic and potential energy, the work-energy theorem, conservation of energy with and without friction, and power.
What the exam asks
- Compute work done by constant forces, including negative work and zero-work cases
- Apply the work-energy theorem to connect net work and speed change
- Use energy conservation across positions (ramps, pendulums, springs, projectiles)
- Account for friction as mechanical energy converted to thermal energy
- Calculate power as the rate of energy transfer
Key formulas and rules
W = F·d·cosθ; area under F-x graph
W(net) = ΔKE
KE = ½mv²; PE(grav) = mgh; PE(spring) = ½kx²
KE1 + PE1 = KE2 + PE2 + f·d
P = W/t = F·v
Question bank breakdown
44
8
12 easy · 24 medium · 8 hard
Skills covered
Every question in the bank comes with a per-choice explanation, so you learn why each wrong answer is wrong — not just the key.
Sample question
From the free tier of the ScoreMint AP Physics 1 bank — try it, then check the answer.
A $4.0 \text{ kg}$ block slides across a rough horizontal surface. Its speed decreases from $6.0 \text{ m/s}$ to $2.0 \text{ m/s}$ over a distance of $4.0 \text{ m}$. What is the magnitude of the friction force acting on the block?
- A. $8.0 \text{ N}$
- B. $16 \text{ N}$
- C. $32 \text{ N}$
- D. $4.0 \text{ N}$
Show answer and explanation
Answer: B. The work-energy theorem states that the net work done on an object equals its change in kinetic energy: $W_{net} = \Delta KE$. Here, $\Delta KE = \frac{1}{2}(4.0)(2.0^2) - \frac{1}{2}(4.0)(6.0^2) = 8 - 72 = -64$ J. The only horizontal force is friction, and its work is $W_f = -fd$ (negative because friction opposes displacement). Setting $-f(4.0) = -64$ J gives $f = 16$ N. The negative sign of $\Delta KE$ confirms energy was removed from the block by friction.
Study tip
Choose energy methods when the question asks about speeds at two positions and forces are messy in between; choose Newton's laws when it asks about forces or acceleration at one instant.