AP Physics AP Physics Rotational Motion & Gravitation 2

Question 1

A figure skater pulls their arms inward during a spin. Their angular velocity:

Accepted Answer

Increases

Answer

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?

Accepted Answer

Gravity

Answer

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:

Accepted Answer

(1/2)Iω²

Answer

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?

Accepted Answer

16 N·m

Answer

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:

Accepted Answer

v = √(GM/r)

Answer

Setting gravitational force equal to centripetal force: GMm/r² = mv²/r gives v = √(GM/r).

AP Practice Test