AP Physics 1 — Unit 3: Work, Energy, and Power
Practice questions, answers, and key terms for Unit 3, aligned to the College Board CED.
AP Physics 1 Unit 3 practice questions
A 2 kg drone flies at 3 m/s. You want its translational kinetic energy. Which relationship gives it?
KE = ½mv² = 9 J here. It scales with speed squared: ½(2)(3²) = 9 J, not with speed itself.
Two cars have the same mass. Car B moves twice as fast as Car A. How does Car B's kinetic energy compare?
Car B has 4× the kinetic energy. KE = ½mv² depends on v², so doubling speed multiplies KE by 2² = 4.
Momentum is a vector with direction. Is translational kinetic energy also a vector you can split into x and y components?
No — kinetic energy is a scalar with magnitude only. You never resolve it into x and y components.
A passenger sits still inside a train moving at 30 m/s. One observer is on the train, another on the platform. Do they measure the same kinetic energy for the passenger?
No — train observer sees KE = 0, platform sees a large KE. KE depends on the observer's reference frame.
A 0.5 kg ball speeds up from 4 m/s to 8 m/s. By how much did its kinetic energy change?
ΔKE = ½(0.5)(8²) − ½(0.5)(4²) = 16 − 4 = 12 J. You compute KE at each speed and subtract — you can't just scale the difference in speeds.
Your friend insists a car parked on a hill has kinetic energy because it's "ready to roll." Where do they go wrong?
Kinetic energy is energy of actual motion (KE = ½mv²). A parked car has v = 0, so KE = 0. "Ready to roll" is gravitational potential energy, not kinetic.
You drag a crate 5 m by pulling with 40 N at 60° above horizontal. How much work do you do on it?
W = Fd·cosθ = 40·5·0.5 = 100 J. Only the force component along displacement does work.
You carry a 10 kg box across a flat floor at constant speed. Your upward carrying force is perpendicular to the horizontal motion. How much work does that force do?
Zero — the carrying force is perpendicular to it. W = Fd·cos90° = 0, so it transfers no energy.
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Key terms in Unit 3
These 12 terms show up in the Unit 3 cards. Each one links to its definition in the AP Physics 1 key-term reference.
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