PHYS chpt. 8

The chef at the infamous Fattening Tower of Pizza tosses a spinning disk of uncooked pizza dough into the air. The disk's diameter increases during the flight, while its rotational speed...

Decreases

A car travels in a circle with constant speed. The net force on the car is...

Directed toward the center of the curve

Door B is twice as wide as door A, but both doors have the same height and the same mass. A person pushes on the edge of the two doors with the same force. Which door opens more quickly?

Door A

If a turntable's rotational speed is doubled, then the linear speed of a pet hamster sitting on the edge of the record will...

Double

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

When the rotational speed of a rotating system doubles, its angular momentum...

Doubles

Your pet hamster sits on a record player whose angular speed is constant. If he moves to a point twice as far from the center, then his linear speed...

Doubles

Neglecting air resistance, which will roll from rest to the bottom of an incline first, an empty jar, or the same jar filled with peanut butter?

The filled jar

To turn a stubborn screw, it is best to use a screwdriver that has a...

Wide handle

Toss a baseball bat into the air and it wobbles about its...

Center of mass

A 1-kg rock is suspended from the tip of a meter stick at the 0-cm mark so that the meter stick balances like a seesaw when the fulcrum is at the 25-cm mark. From this information, what is the mass of the meter stick?

1 kg

A girl weighs 60 pounds and is sitting on the teeter-totter 3 m from the center. How far from the center should a 180-pound boy sit so that the teeter-totter balances?

1 meter

On a balanced seesaw, a boy three times as heavy as his partner sits...

1/3 the distance from the fulcrum

To tighten a bolt, you push with a force of 84N at the end of a wrench handle that is 0.20m from the axis of the bolt. What torque are exerting? 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.

17 N*m 170 N (Answers depend on direction of your push relative to the direction of the wrench handle)

Suppose you're on a Ferris wheel at a carnival, seated 10 m from the Ferris wheel's axis. If you make a complete rotation each minute, your linear speed is...

62.8 m/min.

A baseball bat is balanced on a fulcrum. The center of gravity of the bat is located...

Above the fulcrum

The famous Leaning Tower of Pisa doesn't topple over because its center of gravity is...

Above the place of support

A ball rolls down a hill mainly because of...

An unbalanced torque

The center of gravity of a basketball is located...

At its geometrical center

If the Earth had two identical moons in one circular orbit, and the moons were as far apart in that orbit as they could be, the center of gravity of the Earth-moons system would be...

At the center of the Earth

The center of gravity of a circular disk of sheet metal is...

At the center of the disc

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

External torque

Calculate the tension in a horizontal string that whirls a 1.8-kg toy in a circle of radius 2.5m when it moves at 2.8m/s on an icy surface.

F = 5.6 N B/C - Centripetal force = F=mv^2/r

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

Force and leverage distance

Suppose Sally lived on the equator of a planet that had a radius twice that of Earth's radius and that rotated with twice the angular velocity (so one day would be 12 hours long). Sally's speed on this planet would be _______ Joe's speed (who lives on Earth's equator).

Four times faster than B/C - Sally's angular velocity is twice as high as Joe's, and since Sally is tracing out a circle with twice the radius of Joe's path, Sally is going four times faster than Joe.

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

Greater than toward the center

If the planet Jupiter underwent gravitational collapse, its rate of rotation about its axis would...

Increase

Rotational inertia about the midpoint of an object becomes greater with...

Increased mass and increased distance to mass concentration

When a twirling ice skater brings her arms inward, her rotational speed...

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 greater.

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 farther from your hand.

Joe lives on the equator, and Sally lives in Alaska. Which person has the higher speed due to Earth's rotation?

Joe B/C - The equator is further from the axis of rotation than Alaska.

Joe lives on the equator, and Sally lives in Alaska. Which person has the higher angular velocity due to Earth's rotation?

Joe and Sally have the same angular velocity B/C - they both complete one revolution ever 24 hours

Horses that move with the fastest linear speed on a merry-go-round are locate...

Near the outside.

Which moves faster in m/s on a merry-go-round: a horse on the inside or a horse on the outside near the outer rail?

Outside horse

When a rock tied to a string is whirled in a horizontal circle, doubling the speed...

Quadruples the tension in the string

Suppose you are at the center of a large freely-rotating horizontal turntable in a carnival funhouse. As you crawl toward the edge, the angular momentum of you and the turntable...

Remains the same, but the RPMs decrease.

A huge rotating cloud of particles in space gravitate together to form an increasingly dense ball. As it shrinks in size, the cloud...

Rotates faster

Centrifugal forces are an apparent reality to observers in a reference frame that is...

Rotating

A torque acting on an object tends to produce...

Rotation

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 farther the mass is, the higher the rotational inertia.

A ring, a disk, and a solid sphere begin rolling down a hill together. The one to reach the bottom first is the...

Sphere

A ring and a disk, initially at rest, roll down a hill together. The one to reach the bottom first...

The disk

For a system in mechanical equilibrium...

The resultant forces and torques must both be zero

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 greater than the rotational inertia of the rod with the mass closer to the bottom.

A carnival has a Ferris wheel where the seats are located halfway between the center and outside rim. If you were at the outside rim, your angular speed while riding on this Ferris wheel would be...

The same and your tangental speed more

Put a pipe over the end of a wrench when trying to turn a stubborn nut on a bolt, to effectively make the wrench handle twice as long, you'll multiply the torque by...

Two

Calculate the torque produced by a 42-N perpendicular force at the end of a 0.25-m-long wrench.

r = 11 Nm B/C - Torque = Level arm * Force

To kick a football so it won't topple end over end, kick it so the force of impact extends

through its center of gravity