PHYSIC HW CHP 8

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? A. 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. B. Your center of gravity is too high above your support base. C. A vertical line through the center of gravity of your body is behind your heels, which is outside your support base. D. Your center of gravity does not hang below your support base.

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

A. 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? A. Somewhere straight below where your hands grab the rope B. Somewhere straight above where your hands grab the rope C. Where your hands grab the rope D. At the end of the rope

A. Somewhere straight below where your hands grab the rope

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? A. The tangential speed of the wide end is faster. B. The tangential speed of the wide end is zero. C. The tangential speed of the wide end is slower. D. The tangential speed is the same for both ends.

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

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

How do clockwise and counterclockwise torques compare when a system is balanced? A. They are equal in magnitude and opposite in direction. B. The clockwise torque is greater. C. The counterclockwise torque is greater. D. They are both zero.

A. They are equal in magnitude and opposite in direction.

Where is the center of mass of a baseball? Where is its center of gravity? A.The center of mass and the center of gravity are both at the center of the spherical ball. B. The center of mass is 1 mm above the center of the spherical ball, whereas the center of gravity is 1 mm below. C. The center of mass is at the center of the spherical ball, whereas the center of gravity is 1 mm below that. D.The center of mass is at the center of the spherical ball, whereas the center of gravity is 1 mm above that.

A.The center of mass and the center of gravity are both at the center of the spherical ball.

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

A.The distribution of mass about the axis of rotation

What are the units of measurement for tangential speed? For rotational speed? A.m/s for tangential, RPM for rotational B. RPM for tangential, m/s for rotational C. m/s for both D. RPM for both

A.m/s for tangential, RPM for rotational

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. A. Axis along the lead, through one end, through the center B. Axis along the lead, through the center, through one end C. Axis through one end, along the lead, through the center D. Axis through the center, through one end, along the lead

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

Why does bending your legs when running enable you to swing your legs to and fro more rapidly? A. Bending your legs puts the rotational axis in the center of the leg, thus reducing rotational inertia. B. Bending your legs shortens them, thus reducing rotational inertia. C. Bending your legs decreases the angular speed, thus reducing rotational inertia. D. Bending your legs increases the height of the foot, thus reducing rotational inertia.

B. Bending your legs shortens them, thus reducing rotational inertia.

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? A. Her angular momentum is cut in half. Her spin rate is cut in half. B. Her angular momentum does not change. Her spin rate doubles. C. Her angular momentum is doubled. Her spin rate is doubled. D. Her angular momentum is cut in half. Her spin rate does not change.

B. Her angular momentum does not change. Her spin rate doubles.

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

B. In the center of the ball

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

B. It will rotate about the center of mass.

How is a flywheel constructed to maximize its rotational inertia? A. Most of the mass is concentrated near the axis. B. Most of the mass is concentrated far from the axis. C. Most of the mass is concentrated near a ring half way between the axis and the rim. D. The mass is uniformly distributed across the radius of the disk.

B. Most of the mass is concentrated far from the axis.

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? A. Centrifugal; Newton's third law B. No force; Newton's first law C. Centripetal; Newton's second law. D. Centrifugal; Newton's first law

B. No force; Newton's first law

Which is easier to get swinging: a baseball bat held at the narrow end or a bat held closer to the massive end (choked up)? Also answer for a short bat versus a long bat. A. The easiest is at the narrow end and a short bat. B. The easiest is choked up and a short bat. C. The easiest is choked up and a long bat. D. The easiest is at the narrow end and a long bat.

B. The easiest is choked up and a short bat.

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

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

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? A. Tangent to the circle in the direction of motion of the can B.Toward the center of the circle C.Radially outward from the center of the circle D. Tangent to the circle and opposite in direction to the motion of the can

B.Toward the center of the circle

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

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

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

C. It increases.

Is it an inward force or an outward force that is exerted on the clothes during the spin cycle of an automatic washing machine? What about the direction of the force on the water? A. The force is inward on clothes and outward on water. B. There is no force on clothes and it is outward on water. C. The force is inward on clothes and there is none on water. D. The force is outward on clothes and outward on water.

C. The force is inward on clothes and there is none on water.

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? A. The tangential speed is proportional to the radius. The inside of the wheel rolls on a smaller radius than the outside of the wheel. B. The tangential speed is inversely proportional to the radius. The outside of the rim rolls on a smaller radius than the inside. C. The tangential speed is proportional to the radius. The inside of the wheel rolls on a larger radius than the outside of the wheel. D. The tangential speed is inversely proportional to the radius. The outside of the rim rolls on a larger radius than the inside.

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

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

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

What is the relationship between the center of gravity and the support base for an object that is in stable equilibrium? A. A vertical line through the center of gravity must pass through the center of the support base. B. The center of gravity must be below the support base. C. The center of gravity must be in the center of the support base of the object. D. A vertical line through the center of gravity must pass inside the support base of the object.

D. A vertical line through the center of gravity must pass inside the support base of the object.

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

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

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

D. All of the above

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

D. Angular momentum does not change without an applied external torque.

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

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

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

D.Tangential speed increases with distance. Rotational speed is constant.