exam 2 review

The solid dot shown in the figure below is a pivot point. The board can rotate about the pivot. Which force shown exerts the largest magnitude torque on the board?

(c) 500 N

A 35-N bucket of water is lifted vertically 3.0 m and then returned to its original position. How much work did gravity do on the bucket during this process?

0 J

An object at rest begins to rotate with a constant angular acceleration. If this object rotates through an angle θ in time t, through what angle did it rotate in the time 12t?

1/4θ

A force produces power P by doing work W in a time T. What power will be produced by a force that does six times as much work in half as much time?

12P

Which requires more work, increasing a car's speed from 0 mph to 30 mph or from 50 mph to 60 mph?

50 mph to 60 mph

If the sum of both the external torques and the external forces on an object is zero, then the object must be at rest.

False

If the sum of the external forces on an object is zero, then the sum of the external torques on it must also be zero.

False

If the sum of the external torques on an object is zero, then the sum of the external forces on it must also be zero.

False

A heavy ball suspended by a cable is pulled to the side by a horizontal force F→ as shown in (Figure 1). If angle θ is small, the magnitude of the force F can be less than the weight of the ball because:

F→ is equal to only the x component of the tension in the cable.

The graphs shown show the magnitude F of the force exerted by a spring as a function of the distance x the spring has been stretched. For which one of the graphs does the spring obey Hooke's law?

Graph b

A small mass m on a string is rotating without friction in a circle. The string is shortened by pulling it through the axis of rotation without any external torque (Figure 1). What happens to the angular velocity of the object?

It increases.

A small mass m on a string is rotating without friction in a circle. The string is shortened by pulling it through the axis of rotation without any external torque, see the figure(Figure 1) . What happens to the tangential velocity of the object?

It increases.

Two men, Joel and Jerry, push against a car that has stalled, trying unsuccessfully to get it moving. Jerry stops after 10 min, while Joel is able to push for 5.0 min longer. Compare the work they do on the car.

Neither of them does any work.

Two identical billiard balls traveling at the same speed have a head-on collision and rebound. If the balls had twice the mass, but maintained the same size and speed, how would the rebound be different?

No difference.

A golf ball and an equal-mass bean bag are dropped from the same height and hit the ground. The bean bag stays on the ground while the golf ball rebounds. Which experiences the greater impulse from the ground?

The golf ball.

Two spheres have the same radius and equal mass. One sphere is solid, and the other is hollow and made of a denser material. Which one has the bigger moment of inertia about an axis through its center?

The hollow one.

A heavy dart and a light dart are launched vertically by identical ideal springs. Both springs were initially compressed by the same amount. There is no significant air resistance. Which of the following statements about these darts are correct? (There could be more than one correct choice.)

The light dart goes higher than the heavy dart. At the maximum height, both darts have the same gravitational potential energy.

A stone can slide down one of four different frictionless ramps, as shown in the figure. For which ramp will the speed of the ball be the greatest at the bottom?

The speed of the ball will be the same for all ramps.

You are lying in bed and want to shut your bedroom door. You have a bouncy "superball" and a blob of clay, both with the same mass. Which one would be more effective to throw at your door to close it?

The superball.

Two wheels having the same radius and mass rotate at the same angular velocity ((Figure 1)). One wheel is made with spokes so nearly all the mass is at the rim. The other is a solid disk. How do their rotational kinetic energies compare?

The wheel with spokes has about twice the KE.

If the force on an object is in the negative direction, the work it does on the object must be

The work could be either positive or negative, depending on the direction the object moves.

A truck going 15 km/hkm/h has a head-on collision with a small car going 30 km/hkm/h.

They both have the same change in magnitude of momentum because momentum is conserved.

They have the same momentum, but the car has more kinetic energy than the truck. After you push both the car and the truck for the same distance with the same force, what can you say about the momentum and kinetic energy (KE) of the car and the truck? Ignore friction.

They have the same kinetic energy, but the truck has more momentum than the car.

A small car and a heavy pickup truck are both out of gas. The truck has twice the mass of the car. After you push both the car and the truck for the same amount of time with the same force, what can you say about the momentum and kinetic energy (KE) of the car and the truck? Ignore friction.

They have the same momentum, but the car has more kinetic energy than the truck.

An astronaut is a short distance away from her space station without a tether rope. She has a large wrench. What should she do with the wrench to move toward the space station?

Throw it directly away from the space station.

If an object remains at rest, then the sum of both the external torques and the external forces on the object must be zero.

True

When you apply the torque equation ∑τ=0 to an object in equilibrium, the axis about which torques are calculated

can be located anywhere.

A small boat coasts at constant speed under a bridge. A heavy sack of sand is dropped from the bridge onto the boat. The speed of the boat

decreases.

Jill does twice as much work as Jack does and in half the time. Jill's power output is

four times Jack's power output.

Bonnie sits on the outer rim of a merry-go-round, and Jill sits midway between the center and the rim. The merry-go-round makes one complete revolution every 2 seconds. Jill's linear velocity is:

half of Bonnie's.

If there were a great migration of people toward the Earth's equator, the length of the day would

increase because of conservation of angular momentum.

A railroad tank car contains milk and rolls at a constant speed along a level track. The milk begins to leak out the bottom. The car then

maintains a constant speed.

The space shuttle, in circular orbit around the Earth, collides with a small asteroid which ends up in the shuttle's storage bay. For this collision,

only momentum is conserved.

Two children are balanced on opposite sides of a seesaw. If one child leans inward toward the pivot point, her side will

rise.

If you used 1000 J of energy to throw a ball, would it travel faster if you threw the ball (ignoring air resistance)

so that it wasn't rotating?

Suppose you are sitting on a rotating stool holding a 2-kgkg mass in each outstretched hand. If you suddenly drop the masses, your angular velocity will

stay the same.

Two objects, one of mass m and the other of mass 2m, are dropped from the top of a building. If there is no air resistance, when they hit the ground

the heavier one will have twice the kinetic energy of the lighter one.

When a car is weighed, it is driven slowly on a horizontal floor over a scale that records a reading as the front wheels go over the scale, and then records a second reading as the rear wheels go over the scale. The weight of the car is equal to

the sum of the two weights.