Physics Ch 8

Why doesn't the Leaning Tower of Pisa topple over? The center of gravity is at the center of the building. A vertical line through the center of gravity passes through the center of its support base. The center of gravity is suspended below its support base. A vertical line through the center of gravity passes inside its support base.

A vertical line through the center of gravity passes inside its support base.

How can gravity be simulated in an orbiting space station? Rotate a cylinder to create centrifugal force as viewed by a person on the inside of the curved outer wall Spin two pods connected by a cable Spin a station shaped like a bicycle wheel All of the above

All of the above

Distinguish between linear momentum and angular momentum. Angular momentum depends on tangential velocity, whereas linear momentum depends on the rotational velocity. 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 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 along the lead, through one end, through the center 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 the center, through one end

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

What is required to change the angular momentum of a system? External force External torque Force Torque

External torque

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 cut in half. Her spin rate is cut in half. 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 doubled. Her spin rate is doubled.

Her angular momentum does not change. Her spin rate doubles

Where is the center of mass of a hollow soccer ball? In the center of the 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

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

It decreases.

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

It decreases.

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

It decreases.

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

It increases.

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

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

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 one end. It will rotate about the center of mass. It will rotate about the place it was last touched by your hand.

It will rotate about the center of mass.

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 Centripetal; Newton's second law. Centrifugal; Newton's third law No force; Newton's first law

No force; Newton's first law

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 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 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 farther the mass is, the higher the rotational inertia.

Inertia depends on mass; rotational inertia depends on mass and something else. What? The tangential speed of the rim The distribution of mass along the axis of rotation The angular speed The distribution of mass about the axis of rotation

The distribution of mass about the axis of rotation

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 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.

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? Both will have the same acceleration because they have the same rotational inertia. The solid disk will because it is heavier. The solid disk will because the mass is closer to the axis of rotation. 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.

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 is the same for both ends. The tangential speed of the wide end is slower. The tangential speed of the wide end is faster. The tangential speed of the wide end is zero.

The tangential speed of the wide end is faster.

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? It is centrifugal force as viewed by someone outside the car. There is no force as viewed by someone outside the car. To them you move in a straight line. Centripetal force It is centripetal force, but only as viewed by someone inside the car.

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

What does a torque tend to do to an 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 increase the rotational inertia 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.

The center of gravity of a basketball is located _______. in the material making up its mass at its geometrical center at a point opposite to its center of mass at the point of application when balanced

at its geometrical center

When a rock tied to a string whirled in a horizontal circle somehow doubles in mass but keeps the same speed, the string tension _______. doubles decreases remains the same increases by four

doubles

When the rotational speed of a rotating system doubles, its angular momentum _______. reduces to zero quadruples doubles remains unchanged

doubles

The tangential speed on the outer edge of a rotating carousel is _______. four times as great for twice the distance greater than toward the center less than toward the center the same as toward the center

greater than toward the center

Rotational inertia about the midpoint of an object becomes greater with _______. increased mass and increased distance to mass concentration decreased mass and decreased distance to mass concentration decreased mass increased mass

increased mass and increased distance to mass concentration

When a rock tied to a string is whirled in a horizontal circle, doubling the speed _______. doubles the velocity, but the string tension remains the same quadruples the tension in the string decreases the velocity doubles the tension in the string

quadruples the tension in the string

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

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 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. 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.

Why is centrifugal force in a rotating frame called a "fictitious force"? It is not a fundamental force of nature. Instead, it is a force that only appears in an accelerating frame of reference. Newton made it up. An outside observer has to add in the centrifugal force to understand motion in a rotating frame of reference. It is a force physicists had to insert to make the equations work out right.

It is not a fundamental force of nature. Instead, it is a force that only appears in an accelerating frame of reference.

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 center of mass of an object. 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. It is the distance between the point at which a force is applied and the rotational axis.

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

If you hang at rest by your hands from a long vertical rope, where is your center of gravity with respect to the rope? Somewhere straight above where your hands grab the rope At the end of the rope Where your hands grab the rope Somewhere straight below where your hands grab the rope

Somewhere straight below where your hands grab the rope

On a rotating turntable, how do tangential speed and rotational speed vary with distance from the center? Tangential speed increases with distance. Rotational speed is constant. Both are constant. Rotational speed increases with distance. Tangential speed is constant. Both increase in speed with distance.

Tangential speed increases with distance. Rotational speed is constant.

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? Tangent to the circle in the direction of motion of the can Toward the center of the circle Tangent to the circle and opposite in direction to the motion of the can Radially outward from the center of the circle

Toward the center of the circle

The torque exerted by a crowbar on an object increases with increased _______. rotational inertia force force and leverage distance energy of application

force and leverage distance

What are the units of measurement for tangential speed? For rotational speed? RPM for both m/s for both m/s for tangential, RPM for rotational RPM for tangential, m/s for rotational

m/s for tangential, RPM for rotational