AP Physics AP Physics Rotational Motion & Gravitation 2 — Questions and Answers
Question 1: A figure skater pulls their arms inward during a spin. Their angular velocity:
- Decreases
- Increases (Correct answer)
- Stays the same
- Goes to zero
Correct answer: Increases
Pulling arms inward reduces moment of inertia; since L = Iω is conserved, ω must increase.
Question 2: What provides the centripetal force for a satellite in circular orbit around Earth?
- Normal force
- Tension
- Gravity (Correct answer)
- Friction
Correct answer: Gravity
Gravity acts as the centripetal force that keeps a satellite in circular orbit.
Question 3: The rotational kinetic energy of an object with moment of inertia I and angular velocity ω is:
- Iω
- (1/2)Iω
- (1/2)Iω² (Correct answer)
- Iω²
Correct answer: (1/2)Iω²
Rotational kinetic energy is KE_rot = (1/2)Iω², analogous to (1/2)mv² for linear motion.
Question 4: A torque is applied to a door 0.8 m from the hinge with a 20 N force perpendicular to the door. What is the torque?
- 25 N·m
- 16 N·m (Correct answer)
- 0.04 N·m
- 20 N·m
Correct answer: 16 N·m
Torque τ = rF sin θ = 0.8 × 20 × sin 90° = 16 N·m.
Question 5: For a circular orbit of radius r around Earth (mass M), the orbital speed v is:
- v = √(GM/r) (Correct answer)
- v = √(2GM/r)
- v = GM/r²
- v = √(GMr)
Correct answer: v = √(GM/r)
Setting gravitational force equal to centripetal force: GMm/r² = mv²/r gives v = √(GM/r).
Question 6: Which of the following best describes the work done by torque during an angular displacement θ?
- W = τ/θ
- W = τθ (Correct answer)
- W = τ²θ
- W = τ + θ
Correct answer: W = τθ
The work done by a constant torque over angular displacement θ is W = τθ, analogous to W = Fd.
AP Physics AP Physics Rotational Motion & Gravitation 2
A figure skater pulls their arms inward during a spin.
Their angular velocity: