Review Questions for Lectures 16,17
Conceptual Questions:
1. As a tetherball wraps around its pole, what happens?
a) Does it speed up or slow down? Why?
b) Are any torques being applied?
2. If a net torque is applied to an object, that object will experience:
a. a constant angular velocity.
b. an angular acceleration.
c. a constant moment of inertia.
d. an increasing moment of inertia.
3. A figure skater with arms initially extended starts spinning on the ice
at 3 rad/s. She then pulls her arms in close to her body.
Which of the following results?
a. A smaller rotational rate.
b. A greater rotational rate.
c. A greater angular momentum.
d. A smaller angular momentum.
Numerical Problems: answers link to a help page.
1. A ventilation fan with a moment of inertia of 0.034 kg*m2 has a net torque of 0.11 N*m applied to it. What angular acceleration does it experience?
2. A ventilation fan with a moment of inertia of 0.034 kg*m2 has a net torque of 0.11 N*m applied to it. If it starts from rest, what angular momentum will it have 8.0 s later?
3. A ventilation fan with a moment of inertia of 0.034 kg*m2 has a net torque of 0.11 N*m applied to it. If it starts from rest, what kinetic energy will it have 8.0 s later?
4. A solid sphere of mass 4.0 kg and radius 0.12 m starts from rest at the top of a ramp inclined 15°, and rolls to the bottom. The upper end of the ramp is 1.2 m higher than the lower end. What is the linear velocity of the sphere when it reaches the bottom of the ramp (Note: I = 0.4MR2 for a solid sphere)?
5. An ice skater spins at 2.5 rev/s when his arms are extended. He draws his arms in and spins at 6 rev/s. By what factor does his moment of inertia change in the process?
6. A solid cylinder (I = MR2/2) has a string wrapped around it many times. When I release the cylinder, holding on to the string, the cylinder falls and spins as the string unwinds, yoyo-like. What is the downward acceleration of the cylinder as it falls?
7. An astronaut is on a 100 m life-line outside a spaceship, circling the ship with an angular velocity of 0.1 rad/s. How far can she be pulled in before the centripetal acceleration reaches 5g = 49 m/s2?