Conceptual Physics

Chapter 10 Problems

Conceptual Problems

C.1 (a) Can an object have an angular velocity if there is no net torque acting on it? (b) Can an object have a net torque acting on
it if it has zero angular velocity?

(a) Yes No

(b) Yes No

C.2 On which of the following does the moment of inertia depend?

Angular velocity

Angular momentum

Shape of the object

Location of axis of rotation

Mass

Linear velocity

C.3 An object of fixed mass and rigid shape has one unique value for its moment of inertia. True or false? Explain your answer.

True False

C.4 Compared to a solid sphere, will a hollow spherical shell (like a basketball) of the same mass and radius have a greater or a
lesser moment of inertia for rotations about an axis passing through the center? Explain your answer.

Greater Lesser

C.5 Scoring in the sport of gymnastics has much to do with the difficulty of the skills performed, with higher scores awarded to

more difficult tricks. The position of a gymnast's body in a trick determines the difficulty. There are three positions to hold the

body in a flip: the tuck, in which the legs are bent and tucked into the body; the pike, in which the body is bent at the hips but

the legs remain straight; and the layout, in which the whole body is straight. A layout receives a higher score than a pike

which receives a higher score than a tuck. Use the principles of rotational dynamics to describe why the position of the body

affects the difficulty of a flip.

Section Problems

Section 0 - Introduction

0.1 Use the simulation in the interactive problem in this section to answer the following questions. (a) Does changing the distance
from the axis of rotation affect the angular acceleration? (b) Where should you push to create the maximum torque and
angular acceleration?
(a) Yes No
(b) i. Farthest from the axis of rotation
ii. In the middle of the bridge
iii. Closest to the axis of rotation

Section 1 - Torque

1.1 The wheel on a car is held in place by four nuts. Each nut should be tightened to 94.0 N·m of torque to be secure. If you have

a wrench with a handle that is 0.250 m long, what minimum force do you need to exert perpendicular to the end of the wrench

to tighten a nut correctly?

N

1.2 A 1.1 kg birdfeeder hangs from a horizontal tree branch. The birdfeeder is attached to the branch at a point that is 1.1 m from

the trunk. What is the amount of torque exerted by the birdfeeder on the branch? The origin is at the pivot point, where the

branch attaches to the trunk.

N·m

1.3 Bob and Ray push on a door from opposite sides. They both push perpendicular to the door. Bob pushes 0.63 m from the
door hinge with a force of 89 N. Ray pushes 0.57 m from the door hinge with a force of 98 N, in a manner that tends to turn
the door in a clockwise direction. What is the net torque on the door?
N·m

Section 2 - Torque, moment of inertia and angular acceleration

2.1 The pulley shown in the illustration has a radius of 2.70 m and a moment of inertia of 39.0 kg·m^2. The hanging mass is

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