AP Review: Rotational Motion & Torque

A disc has a radius of 5 cm. If the disc rotates about its central axis at an angular speed of 8 rev/s, what is the linear speed of a point on the rim of the disc?

• 0.4 m/s

• 2.5 m/s

• 3.9 m/s

• 50 m/s

An object, initially at rest, begins spinning under a constant angular acceleration. In 15 s, it completes an angular displacement of 90 rad. What is the magnitude of the angular acceleration it experiences?

• 0.4 rad/s²

• 0.8 rad/s²

• 6 rad/s²

• 12 rad/s²

A wheel initially rotating at 12 rad/s decelerates uniformly to rest in 0.4 s. If the wheel has a rotational inertia of 0.5 kg*m², what is the magnitude of the torque causing this deceleration?

• 1.5 m*N

• 15 m*N

• 30 m*N

• 38 m*N

A grinding whell with a radius of 12 cm is being used to sharpen a knife. The side of the knife is pressed perpendicularly into the wheel's surface with a force of 16 N. The coefficient of kinetic friction between the knife and the wheel is 0.28. What is the torque the grinding wheel's motor must supply to maintain its rotation rate of 50 rad/s?

• 0.50 m*N

• 0.72 m*N

• 4.5 m*N

• 54 m*N

A uniform 10 m ladder with a mass of 20 kg rests against a wall such that it makes a 50^o angle with the ground. IF the friction between the ladder and the wall is negligible, what is the force the ladder exerts on the wall?

• 82 N

• 98 N

• 164 N

• 196 N

A child with a mass of 25 kg is standing at the edge of a 2.0 m radius merry-go-round., and they are rotating without friction at 20 rpm. The child then moves toward the center of the merry-go-round. The merry-go-round has a rotational inertia of 1,200 kg*m², and the rotational inertia is I = mr², where r is her distance from the axis of rotation. What is the new angular velocity when she is 0.5 m from the center of the merry-go-round?

• 2.03 rad/s

• 2.09 rad/s

• 2.15 rad/s

• 2.25 rad/s

In an effort to tighten a bolt, a force F is applied. If the distance from the end of the wrench to the center of the bolt is 20 cm and F = 20 N, what is the magnitude of the torque produced by F?

• 1 m*N

• 2 m*N

• 4 m*N

• 10 m*N

In the figure shown, what is the torque about the pendulum's suspension point produced by the weight of the bob, given that the length of the pendulum, L, is 80 cm and m = 0.50 kg?

• 0.5 m*N

• 1.0 m*N

• 1.7 m*N

• 2.0 m*N