Physics Chapter 8

To tighten a bolt, you push with a force of 90 N at the end of a wrench handle that is 0.25 m from the axis of the bolt. If you move your hand inward to be only 0.10 m from the bolt, find the force that you should exert to achieve the same torque.

F= 230 N

What does a torque tend to do to an object? Torque tends to increase the rotational inertia of the object. Torque tends to increase the linear speed of the object. Torque tends to twist or change the state of rotation of the object. Torque tends to decrease the rotational inertia of the object.

Torque tends to twist or change the state of rotation of the object.

How does the force needed to turn the wrench will change if you increase the lever arm? It increases. It decreases. It stays the same.

it decreases

How does the lever arm will change when you decrease the distance? It stays the same. It increases. It decreases.

it decreases

How does the magnitude of the lever arm will change if you decrease the angle? It decreases. It stays the same. It increases.

it decreases

The rock and meterstick balance at the 25-cm mark, as shown. The meterstick has a mass of 1.4 kg . What must be the mass of the rock?

m= 1.4 kg

The diameter of the base of a tapered drinking cup is 6.8 cm . The diameter of its mouth is 8.8 cm . The path of the cup curves when you roll it on the top of a table. Which end, the base or the mouth, rolls faster?

the mouth.

To tighten a bolt, you push with a force of 90 N at the end of a wrench handle that is 0.25 m from the axis of the bolt. Do your answers depend on the direction of your push relative to the direction of the wrench handle?

yes

To tighten a bolt, you push with a force of 90 N at the end of a wrench handle that is 0.25 m from the axis of the bolt. What torque are you exerting?

τ = 23 N*m

Why can't you stand with your heels and back to a wall and then bend over to touch your toes and return to your stand-up position? Your center of gravity is too high above your support base. A vertical line through the center of gravity of your body is behind your heels, which is outside your support base. A vertical line through the center of gravity of your body is in front of the tips of your toes, which is outside your support base. Your center of gravity does not hang below your support base.

A vertical line through the center of gravity of your body is in front of the tips of your toes, which is outside your support base.

What is the law of inertia for rotating systems in terms of angular momentum? Angular momentum does not change without an applied internal torque. Angular momentum does not change without a change in rotational inertia. Angular momentum does not change without a change in rotational velocity. Angular momentum does not change without an applied external torque.

Angular momentum does not change without an applied external torque.

Where is the center of mass of a hollow soccer ball? At the top-dead-center of the ball At the lowest point of the ball Halfway between the center and the lowest point of the ball In the center of the ball

In the center of the ball.

If the string that holds a whirling can in its circular path breaks, what kind of force causes it to move in a straight- line path: centripetal, centrifugal, or no force? What law of physics supports your answer? Centrifugal; Newton's first law Centrifugal; Newton's third law No force; Newton's first law Centripetal; Newton's second law.

No force; Newton's first law.

Distinguish between linear momentum and angular momentum. Angular momentum depends on the distribution of mass times the total mass, whereas linear momentum depends only on the distribution of mass. Angular momentum depends on tangential velocity, whereas linear momentum depends on the rotational velocity. Angular momentum depends on the total mass, whereas linear momentum depends on the distribution of mass. Angular momentum depends on the distribution of mass, whereas linear momentum depends on the total mass.

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

Consider three axes of rotation for a pencil: along the lead, at right angles to the lead at the middle, and at right angles to the lead at one end. Rate the rotational inertias about each axis from smallest to largest. Axis through the center, through one end, along the lead Axis through one end, along the lead, through the center Axis along the lead, through one end, through the center Axis along the lead, through the center, through one end

Axis along the lead, through the center, through one end.

Earth is not spherical but bulges at the equator. Jupiter bulges more. What is the cause of these bulges?

In accord with Newton's first law, moving things tend to travel in straight lines. Surface regions of a rotating planet tend to fly off tangentially, especially at the equator where tangential speed is greatest. More predominantly, the surface is also pulled by gravity toward the center of the planet. Gravity wins, but bulging occurs at the equator because the tendency to fly off is greater there. Hence a rotating planet has a greater diameter at the equator than along the polar axis.

As distance increases between most of the mass of an object and its center of rotation, how does rotational inertia change? It goes to zero. It decreases. It increases. It stays the same.

It increases.

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? It is easier for the performer to balance a long rod held vertically with people at the other end because the rotational inertia is smaller. It is easier for the performer to balance a long rod held vertically without people at the other end because the rotational inertia is smaller. 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. It is easier for the performer to balance a long rod held vertically without people at the other end because the rotational inertia is greater.

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.

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? Rotational inertia depends on whether the mass is lower or higher. Objects where the mass is higher have a greater rotational inertia. Rotational inertia depends on whether the mass is farther or closer to the point of rotation. The closer the mass is, the higher the rotational inertia. 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.

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.

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? The rotational inertia of the rod with the mass closer to the top is equal to the rotational inertia of the rod with the mass closer to the bottom. 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. The rotational inertia of the rod with the mass closer to the bottom is greater than the rotational inertia of the rod with the mass closer to the top

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.

Which will have the greater acceleration rolling down an incline: a hoop or a solid disk? Why? The hoop will because the mass is furthest from the axis of rotation. The solid disk will because the mass is closer to the axis of rotation. The solid disk will because it is heavier. Both will have the same acceleration because they have the same rotational inertia.

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

A tapered cup rolled on a flat surface makes a circular path. What does this tell you about the tangential speed of the rim of the wide end of the cup compared with that of the rim of the narrow end? The tangential speed of the wide end is zero. The tangential speed of the wide end is slower. The tangential speed is the same for both ends. The tangential speed of the wide end is faster.

The tangential speed of the wide end is faster.

If you toss a stick into the air, it appears to wobble all over the place. Specifically, about what place does it wobble? It will rotate about the center of mass. It will rotate about one end. It will rotate about the place it was last touched by your hand.

it will rotate about the center of mass

If a skater who is spinning pulls her arms in so as to reduce her rotational inertia by half, by how much will her angular momentum change? By how much will her rate of spin change? Her angular momentum is doubled. Her spin rate is doubled. Her angular momentum does not change. Her spin rate doubles. Her angular momentum is cut in half. Her spin rate does not change. Her angular momentum is cut in half. Her spin rate is cut in half.

Her angular momentum is cut in half. Her spin rate does not change.

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? It is easier when the mass is closer to your hand. It is equally easy in both cases. It is easier when the mass is farther from your hand.

It is easier when the mass is farther from your hand.

What is meant by the "lever arm" of a torque? It is the distance between the point at which a force is applied and the rotational axis. It is the distance between the point at which a force is applied and the center of mass of an object. It is the perpendicular distance from the rotational axis to the line along which the force acts. It is the angle between the applied force vector and the rotational axis.

It is the perpendicular distance from the rotational axis to the line along which the force acts.

A small space telescope at the end of a tether line of length L moves at linear speed v about a central space station. If the initial linear speed of the telescope is 1.5 m/s , what is its speed when pulled in to one-third its initial distance from the space station?

4.5 m/s

How does the tapered rim of a wheel on a railroad train allow one part of the rim to have a greater tangential speed than another part when it is rolling on a track? The tangential speed is proportional to the radius. The inside of the wheel rolls on a larger radius than the outside of the wheel. The tangential speed is proportional to the radius. The inside of the wheel rolls on a smaller radius than the outside of the wheel. The tangential speed is inversely proportional to the radius. The outside of the rim rolls on a smaller radius than the inside. The tangential speed is inversely proportional to the radius. The outside of the rim rolls on a larger radius than the inside.

The tangential speed is proportional to the radius. The inside of the wheel rolls on a larger radius than the outside of the wheel.

The diameter of the base of a tapered drinking cup is 6.8 cm . The diameter of its mouth is 8.8 cm . The path of the cup curves when you roll it on the top of a table. How much faster?

v(sub m)/ v(sub b) =1.3

A small space telescope at the end of a tether line of length L moves at linear speed v about a central space station. What will be the linear speed of the telescope if the length of the line is reduced to 0.33 L?

v(sub new)= v/0.33