physics chapter 6 test: work and energy

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

A 35-N bucket of water is lifted vertically 3m and then returned to its original position. How much work did gravity do on the bucket during this process?

0 J

Person X pushes twice as hard against a stationary brick wall as person Y. Which one of the following statements is correct?

Both do zero work

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

You throw a baseball straight up. Compare the sign of the work done by gravity while the ball goes up with the sign of the work done by gravity while it goes down.

The work is negative on the way up and positive on the way down

Which one has larger kinetic energy: a 500-kg object moving at 40 m/s or a 1000-kg object moving at 20 m/s?

The 500-kg object

You slam on the brakes of you car in a panic, and skid a certain distance on a straight level road. If you had been traveling twice as fast, what distance would the car have skidded, under the same conditions?

It would have skidded 4 times farther

A stone is held at a height h above the ground. A second stone with four times the mass of the first one is held at the same height. The gravitational potential energy of the second stone compared to that of the first stone is

four times as much

You and your friend, who weighs the same as you, want to go to the top of the Eiffel Tower. Your friend takes the elevator straight up. You decide to walk up the spiral stairway, taking longer to do so. Compare the gravitational potential energy of you and your friend, after you both reach the top.

Both of you have the same amount of gravitation potential energy at the top

A heavy rock and a light rock are dropped form the same height and experience no significant air resistance as they fall. Which of the following statements about these rocks are correct?

Both rocks have the same speed when they reach the ground

When they reach the ground, the heavier rock has more kinetic energy than the lighter rock

How much KE does a 0.30 kg stone have if it is thrown at 44 m/s?

290 J

A truck has four times the mass of a car and is moving with twice the speed of the car. If Kt and Kc refer to the KE's of the truck and the car, it is correct to say that

Kt=16Kc

Three cars (car F, car G, and car H) are moving w the same speed and slam on their brakes. The most massive car is F, and the least massive is car H. If the tires of all three cars have identical coefficients of kinetic friction w the road surface, which car travels the longest distance to skid to a stop?

They all travel the same distance in stopping

A 4.0 kg object is moving w speed 2.0 m/s. A 1.0 g object is moving w speed 4.0 m/s. Both objects encounter the same constant braking force, and are brought to rest. Which object travels the greater distance before stopping?

Both objects travel the same distance

You slam on the brakes of your car in a panic, and skid a certain distance on a straight level road. If you had been traveling twice as fast., what distance would the car have skidded, under the same conditions?

It would have skidded 4 times farther

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

50 mph to 60 mph

How much work would a child do while pulling a 12-kg wagon a distance of 4.3 m with a 22 N force?

95 J

A child does 350 J of work while pulling a box from the ground up to his tree house at a steady speed w a light rope. The tree ouse is 4.0 m above the ground. What is the mass of the box?

8.9 kg

You carry a 7.0 kg bag of groceries 1.2 m above the ground at constant speed across a 2.7 m room. How much work do you do on the bag in the process?

0 J

A stone w a mass of 1 kg is tied to the end of a light string which keeps it moving in a circle w a constant speed of 4 m/s on a perfectly smooth horizontal tabletop. The radius of the path is 0.60 m. How much work does the tension in the string do on the stone as it makes one-half of a complete circle?

0 J

A traveler pulls on a suitcase strap at an angle 36 degrees above the horizontal. If 555J of work are done by the strap while moving the suitcase a horiz distance of 15 m, what is the tension in the strap?

46 N

A heavy dart and a light dart are launched horizontally on a frictionless table by identical ideal springs. Both springs were initially compressed by the same amount. Which of the following statements about these darts are correct?

The lighter dart leaves the spring moving faster than the heavy dart

The darts both have the same kinetic energy just as they move free of the spring.

Both darts had the same initial elastic potential energy.

When you drop a pebble from height H, it reaches the ground with speed V assuming there is no air resistance. From what height should you drop it so it will reach the ground with twice the speed?

4H

When you throw a pebble straight up with initial speed V, it reaches a maximum height

H assuming there is no air resistance. At what speed should you throw it up vertically

so it will go twice as high?

root 2 V

Two objects, one of mass m and the other of mass 2m, are dropped from the top of a building. When they hit the ground

the heavier one will have twice the KE of the lighter one

Two frisky otters slide down frictionless hillsides of the same height but different

slopes. The slope of the hill of otter 1 is 30°, while the slope of the hill of otter 2 is 60°.

If both start from rest, which otter is moving faster when she reaches the bottom of her

hill?

Both otters have the same speed at the bottom

A lightweight object and a very heavy object are sliding with equal speeds along a level

frictionless surface. They both slide up the same frictionless hill with no air resistance.

Which object rises to a greater height?

They both slide to exactly the same height

A person stands on the edge of a cliff. She throws three identical rocks with the same

speed. Rock X is thrown vertically upward, rock Y is thrown horizontally, and rock Z is

thrown vertically downward. If the ground at the base of the cliff is level, which rock

hits the ground with the greatest speed if there is no air resistance?

They all hit the ground with the same speed.

Joe and Bill throw identical balls vertically upward. Joe throws his ball with an initial

speed twice as high as Bill. Assuming there is no air resistance, the maximum height of

Joe's ball will be

four times that of Bill's ball.

Two cyclists who weigh the same and have identical bicycles ride up the same

mountain, both starting at the same time. Joe rides straight up the mountain, and Bob

rides up the longer road that has a lower grade. Joe gets to the top before Bob. Ignoring

friction and wind resistance, which one of the following statements is true?

The amount of internal energy converted to gravitational potential energy of the

system Joe- Earth is equal to the amount of internal energy converted to

gravitational potential energy of the system Bob-Earth, but the average power of

the process for Joe is greater than that for Bob.

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

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

The resultant force on an object over a 0.50-s time interval is plotted in the graph in the figure. How much work did this force do on the object during the 0.50-s interval?

0 J

A force acts on an object, causing it to move parallel to the force. The graph in the figure shows this force as a function of the position of the object. How much work does the force do as the object moves from 4 m to 6 m?

20 J

A bead is moving with a speed of 20 m/s at position A on the track shown in the figure. This track is friction-free, and there is no appreciable air resistance. What is the speed of the bead at point C?

34 m/s

Swimmers at a water park have a choice of two frictionless water slides, as shown in the figure. Although both slides drop over the same height h, slide 1 is straight while slide 2 is curved, dropping quickly at first and then leveling out. How does the speed v1 of a swimmer reaching the bottom of slide 1 compare with v2, the speed of a swimmer reaching the end of slide 2?

v1 = v2

If the units of your answer are kg ∙ m2/s3, which of the following types of quantities could your answer be? (There could be more than one correct choice.)

power

How large a net force is required to accelerate a 1600-kg SUV from rest to a speed of 25 m/s in a distance of 200 m?

2500 N

If the work done to stretch an ideal spring by 4.0 cm is 6.0 J, what is the spring constant (force constant) of this spring?

7500 N/m

An object with a mass of 10 kg is initially at rest at the top of a frictionless inclined plane that rises at 30° above the horizontal. At the top, the object is initially 8.0 m from the bottom of the incline, as shown in the figure. When the object is released from this position, it eventually stops at a distance d from the bottom of the inclined plane along a horizontal surface, as shown. The coefficient of kinetic friction between the horizontal surface and the object is 0.20, and air resistance is negligible. Find the distance d

20 m

A softball player catches a ball of mass m, which is moving towards her with horizontal speed V.

mV2/(2d)

A disc, a sphere and a ring start rolling down an incline at the same time. They all have the same mass and diameter. In what order will they reach the bottom of the incline.

sphere, disk, hoop

A ball falls to the ground from height h and bounces to height h′. Momentum is conserved in the ball-earth system

no matter what height h′ it reaches.

For a force to be a conservative force, when applied to a single test body

no work must be done for motion in closed paths.