Unit 4 Test

Question 1

Which of the following is not a unit of work?

Answer 1

J⋅m

Question 2

Which of the following is not correct?

Answer 2

The work done by gravity is always negative.

Question 3

Two identical boxes are moved in equal distances in the horizontal direction. Box A experiences a constant net force F applied at an angle θ to the horizontal and box B experiences a constant net force of 2 F applied at an angle of 2 θ to the horizontal. Which of the following is correct?

Answer 3

The amount of work done on each box cannot be determined from the data given.

Question 4

The work done by a variable force F of the form F = kx where x varies from x0 to x1 where x0 = 0 is given by which of the following?

Answer 4

(1/2)kx1^2

Question 5

If a spring is compressed 2.0 cm from its equilibrium position and then compressed an additional 4.0 cm, how much more work is done in the second compression than in the first?

Answer 5

eight times as much

Question 6

Which of the following is a form of Hooke’s law, where Fs  is a spring force?

Answer 6

Fs = –kx

Question 7

Consider a spring that is stretched from its equilibrium position x0, where x0 = 0, to a position x, where x is positive. Which of the following describes why the work done by a spring is negative?

Answer 7

All of the choices are correct.

Question 8

A boat pulls a water skier who weighs 127 lbs at a constant speed. The tension in the ski rope is 125 N. The skier makes a run that is 0.7 km down a long straight river. What is the work done by the water skier on the boat?

Answer 8

−8.75 × 10^4 N • m

Question 9

Which of the following is not a unit of power?

Answer 9

Watt / second

Question 10

Which of the following objects has the greatest kinetic energy?

Answer 10

an object of mass 2m and speed 3v

Question 11

The work done to accelerate a car from 0 m / s to 40 m / s is _____ times greater than the work done to accelerate it from 0 m / s to 20 m / s?

Answer 11

four

Question 12

A mass m is dropped from rest to the ground from a height h. Which of the following is correct?

Answer 12

When it strikes the ground the speed of the mass is independent of m.

Question 13

Assume that when the brakes are applied a constant frictional force is exerted on the wheels of a car. Which of the following is correct?

Answer 13

The distance the car travels before coming to rest is proportional to the square of the speed of the car just before the brakes are applied.

Question 14

Which of the following is not a vector quantity?

Answer 14

power

Question 15

A roller coaster has 8 cars, each of mass of 95.0 kg. The first hill of the ride is 24.8 m above the ground. Which of the following is the gravitational potential energy of the train once the last car had reached the top of the hill?

Answer 15

1.85x10^5 J

Question 16

A roller coaster has eight cars, each of mass of 95.0 kg. The ride begins 47.5 m above the ground. Which of the following is the speed of the train as it encounters a section of track that is 30.0 m below the ride’s starting point? Assume that the train starts from rest.

Answer 16

24.3 m/s

Question 17

If y = 0 is chosen to be at the ground level, which of the following is the gravitational potential energy of a 500 lb weight that was lifted 3.00 ft?

Answer 17

1.50x10^3 ft-lb

Question 18

A spring stretches by 7.00 cm when a force of 50.0 N is applied. Which of the following is the potential energy stored in the spring when it is stretched 10.0 cm?

Answer 18

3.57 J

Question 19

When applied to a system, a nonconservative force _____________.

Answer 19

cannot generate potential energy with the system.

Question 20

It requires 1000 J of work to stretch a spring 3.00 cm. Which of the following is the change in potential energy and the spring constant of the spring?

Answer 20

increase in potential energy = 1000 J

spring constant = 2.22x10^6 N/m

Question 21

A pendulum bob has mass of 0.750 kg and is on a pendulum arm of length 1.00 m. The pendulum is pulled back so that the arm makes an angle of 60.0° from the vertical and is then released. Which of the following is the speed of the mass when it reaches its lowest point?

Answer 21

3.13 m/s

Question 22

A train is on an incline and has a mass of 2.36 × 103 kg. It initially coasts at 27.8 m/s. Which of the following is the speed of the train at position B. Assume no additional assistance from the engine.

Answer 22

34.2 m/s

Question 23

An automobile of mass 900 kg is moving at a speed of 12.5 m/s when it encounters a hill. At the bottom of the hill the car speed increases to 14.6 m/s. If the elevation of the hill is 15.3 m, how much work did the brakes do while going down the hill?

Answer 23

-1.09*10^5 J

Question 24

A steel playground slide is 5.25 m long and is raised 2.75 m on one end. A 45.0 kg child slides down from the top starting at rest. The final speed of the child at the bottom is 6.81 m/s. Find the average force of friction between the child and the slide.

Answer 24

31.7 N

Question 25

A 200 g plastic ball is at rest on a frictionless incline 0.658 m above the surface of a table. The ball then rolls down the incline and across the table, coming to rest after a distance of 2.45 m. Which of the following the average friction on the ball while rolling across the table.

Answer 25

0.527 N