PSSI: Exam 1

A woman lifts a box from the floor. She then moves with constant speed to the other side of the room, where she puts the box down. How much work does she do on the box while walking across the floor at constant speed?

0 J

A 5.0-kg blob of clay moving at 2.0 m/s slams into a 4.0-kg blob of clay at rest. The speed of the two blobs stuck together after colliding is about

1.1 m/s

A rock is thrown vertically into the air. At the top of its path, its acceleration in meters per second per second is about

10

The gain in speed each second for a freely falling object is about

10 m/s

A car moves 4 times as fast as another identical car. Compared to the slower car, the faster car has

16 times the KE

If a power plant is 30% efficient, and the transmission system that delivers power to consumers is 60% efficient, then the overall efficiency is

18%

A 2-kg mass has 40 J of potential energy with respect to the ground. Approximately how far is it located above the ground?

2 m

A 300-kg bear grasping a vertical tree slides down at constant velocity. The friction force between the tree and the bear is

3000 N

A man weighing 800 N stands at rest on two bathroom scales so that his weight is distributed evenly over both scales. The reading on each scale is

400 N

A 5-kg fish swimming at a speed of 1 m/s swallows an absent-minded 1-kg fish at rest. The speed of the larger fish after lunch is

5/6 m/s

A piece of taffy slams into and sticks to another identical piece of taffy that is at rest. The momentum of the two pieces stuck together after the collision is the same as it was before the collision, but this is not true of the kinetic energy, which is partly turned into heat. What percentage of the kinetic energy is turned into heat?

50%

If an object falls with constant acceleration, the velocity of the object must

Continually change by the same amount each second

Bullets are fired from an airplane in the forward direction of motion. The momentum of the airplane will be

Decreased

A skydiver jumps from a high-flying plane. As her velocity of fall increases, her acceleration

Decreases

When an object falls through the air, its velocity increases and its acceleration

Decreases

Compared with the force that brings a small car to a stop, the force required to bring a heavy truck traveling at the same speed to a stop

Depends on the time involved

An elephant and a feather fall from a tree through the air to the ground below. The amount of air-resistance force is greater on the

Elephant

An object at rest may have

Energy

A player hits a ball with a bat. The action force is the impact of the bat against the ball. The reaction to this force is the

Force of the ball against the bat

A car that travels twice as fast as another when braking to a stop will skid

Four times as far

One object that has twice as much mass as another object also has twice as much

Inertia

A rock is thrown vertically into the air. At the very top of its trajectory the net force on it is

Its weight

Two pool balls, each moving at 2 m/s, roll toward each other and collide. Suppose after bouncing apart, each moves at 4 m/s. This collision violates conservation of

Kinetic energy

A force is a vector quantity because it has both

Magnitude and direction

If the speed of a moving object doubles, then what else doubles?

Momentum

A ball is thrown vertically into the air. Because of air resistance, its time coming down compared to its time going up is

More

An object that has kinetic energy must be

Moving

A sandbag is motionless in outer space. A second sandbag with 3 times the mass moving at 12 m/s collides with it and they both stick together, and move at a speed of - 3 m/s - None of these - 4 m/s - 6 m/s - 8 m/s

None of these

Compared with a 1-kg block of solid iron, a 2-kg block of solid iron has the same - All of these - Mass - Weight - None of these - Volume

None of these

The force exerted on the tires of a car to directly accelerate it along a road is exerted by the

Road

A bullet is dropped from the top of the Empire State Building while another bullet is fired downward from the same location. Neglecting air resistance, acceleration is greatest for the

Same for each

A flower pot of mass m falls from rest to the ground below, a distance h. Which statement is correct?

The KE of the pot when it hits the ground is proportional to h

A rocket becomes progressively easier to accelerate as it travels upward from the ground mainly because

The mass of the rocket decreases as fuel is burned

Compared with the mass of a certain object on Earth, the mass of the same object on the Moon is

The same

Neglecting friction, a large block of ice and a small block of ice start sliding down an incline together. The heavier block will get to the bottom

The same time as the light block

Someone standing at the edge of a cliff throws one ball straight up and another ball straight down at the same initial speed. Neglecting air resistance, the ball to hit the ground below the cliff with the greatest speed will be the one initially thrown

They will both hit with the same speed

Galileo's interpretation of motion differed from Aristotle's in that Galileo emphasized

Time rates

If you push an object twice as far while applying the same force, you do

Twice as much work

The force required to maintain an object at a constant velocity in free space is equal to

Zero

When a falling object has reached its terminal velocity, its acceleration is

Zero

Disregarding air resistance, objects fall at constant

Acceleration

Hang from a pair of gym rings and the upward support forces of the rings will always

Add up to equal your weight

A heavy pile driver starting from rest falls on a pile with a force that depends on the - None of these - Original height of the driver - Original potential energy of the driver - All of these - Distance the pile falls

All of these

A moving object has - Speed - Energy - Momentum - All of these - Velocity

All of these

Which has zero acceleration? An object - Moving at constant velocity - None of these - In mechanical equilibrium - All of these - At rest

All of these

Earth pulls on the Moon. Similarly the Moon pulls on Earth, evidence that - Earth's and Moon's pulls comprise an action-reaction pair - Earth and the Moon are simply pulling on each other - Both of these

Both of these

The amount of frection that occurs when two material surfaces slide against each other depends on - How much they are pressed together - The "stickiness" of atoms on their surfaces - Both of these - None of these

Both of these

Which requires more work: lifting a 50-kg sack vertically 2 m or lifting a 25-kg sack vertically 4 m?

Both required the same amount of work

A bullet is fired straight down from the top of a high cliff. Neglecting air resistance, the acceleration of the bullet in meters per second per second is

g