Physics hw 8

What must be the mass of the rock?

0.70 kg

Calculate the torque produced by a 52-N perpendicular force at the end of a 0.24-m-long wrench.

12

If a trapeze artist rotates once each second while sailing through the air and contracts to reduce her rotational inertia to one-third of what it was, how many rotations per second will result?

3

A person having a mass of 65 kg sits on the edge of a horizontal rotating platform, 2.5 m from the center of the platform, and has a tangential speed of 2.8 m/s. Calculate the angular momentum of the person.

460 kg⋅m2s

Which will have the greater acceleration rolling down an incline-a bowling ball or a volleyball? Defend your answer.

A bowling ball, because a solid sphere has less rotational inertia per mass than other shapes. Its mass is near the rotational axis that extends through its center of mass.

A) Is it easier to balance a long rod with a mass attached to it when the mass is closer to your hand or when the mass is farther away? B) How does the rotational inertia of the rod with the mass toward the bottom compare with the rotational inertia of the mass toward the top? C) Why does the rotational inertia of the rod with the attached mass closer to your hand compare the way it does with the rotational inertial of the rod with the attached mass farther away? D) Is it easier for a circus performer to balance a long rod held vertically with people hanging off the other end, or the same long rod without the people at the other end, and why?

A) It is easier when the mass is farther from your hand. B) The rotational inertia of the rod with the mass closer to the top is greater than the rotational inertia of the rod with the mass closer to the bottom. C) Rotational inertia depends on whether the mass is farther or closer to the point of rotation. The farther the mass is, the higher the rotational inertia. D) It is easier for the performer to balance a long rod held vertically with people at the other end because the rotational inertia is greater.

A) Which of the following statements correctly describes the system shown in the figure? B) What happens when block B moves downward?

A) The angular acceleration of the pulley is nonzero. B) The cord's tension on the right side of the pulley is higher than on the left side.

A) Where is the center of gravity of the broom that Dr. Hewitt holds up B) When Dr. Hewitt cuts the broom right through the center of gravity, how do the weights of the two sides of the broom compare? C) How does the torque due to the weight of one side of the broom exerted around the balance point compare with the torque exerted by the weight of the other side of the broom around the balance point?

A) at the balance point B) The shorter side, where the bristles of the broom are, has a greater weight than the handle. C) The torque due to the weight of the shorter side (the bristles of the broom) is equal in magnitude to the torque due to the weight of the longer side, and opposite in direction.

A) How does the lever arm change if you decrease the angle of the force? B) How does the lever arm change when you decrease the distance to the nut? C) How does the force needed to turn the wrench change if you increase the lever arm?

A) decreases B) decreases C) decreases

Identify the cause of this force.

Acceleration caused this force.

Rank the cups by the amount they depart from a straight-line path (most curved to least curved).

B, C, A

Rank the torque needed to keep the stick steady, from largest to smallest.

B, C, A

The experimenter from the video rotates on his stool, this time holding his empty hands in his lap. You stand on a desk above him and drop a long, heavy bean bag straight down so that it lands across his lap, in his hands. What happens?

He spins slower.

How is a flywheel constructed to maximize its rotational inertia?

Most of the mass is concentrated far from the axis.

You sit at the middle of a large turntable at an amusement park as it is set spinning and then allowed to spin freely. When you crawl toward the edge of the turntable, does the rate of the rotation increase, decrease, or remain unchanged? What physics principle supports your answer?

The rate of rotation decreases. The rate of rotation decreases as you crawl out to the rim while rotational inertia increases is accordance with the conservation of angular momentum.

Which will have the greater acceleration rolling down an incline: a hoop or a solid disk? Why?

The solid disk will because the mass is closer to the axis of rotation.

If you are not wearing a seat belt in a car that rounds a curve, and you slide across your seat and slam against a car door, what kind of force is responsible for your slide: centripetal, centrifugal, or no force?

There is no force as viewed by someone outside the car. To them you move in a straight line.

What is required to change the angular momentum of a system?

external torque

The torque exerted by a crowbar on an object increases with increased

force and leverage distance

The tangential speed on the outer edge of a rotating carousel is

greater than toward the center

The center of gravity of a basketball is located

its geometrical center

In the video, the torque due to the mass of the plank is used in the calculations. For this question, ignore the mass of the board. Rank, from largest to smallest, the mass m needed to keep the board from tipping over.

left to right : D, B&A, C, E

The centers of gravity of the three trucks parked on a hill are shown by the Xs. Which truck(s) will tip over?

the left truck

When you whirl a can at the end of a string in a circular path, what is the direction of the force you exert on the can?

toward the center of the circle

Distinguish between linear momentum and angular momentum.

Angular momentum depends on the distribution of mass, whereas linear momentum depends on the total mass.