## Homework Helpers: Physics

## 3 Work, Energy, Power, and Momentum

### Chapter 3 Examination

**Part I—Matching**

Match the following terms to the definitions that follow.

a. work

b. energy

c. kinetic energy

d. gravitational potential energy

e. elastic potential energy

f. mechanical energy

g. power

h. momentum

i. impulse

_______1.__ The rate at which work is done.

_______2.__ The sum of the kinetic and all the forms of potential energy.

_______3.__ The product of an object”s mass and velocity.

_______4.__ The energy that an object possesses due to its motion.

_______5.__ The product of the force and the period of time during which the force is acting.

**Part II—Multiple Choice**

For each of the following questions, select the best answer.

__6.__ Which of the following are units of power?

a) joules

b) watts

c) newtons

d) kg × m/s^{2}

__7.__ If the velocity of a moving car is doubled, its kinetic energy will be

a) halved

b) doubled

c) tripled

d) quadrupled

__8.__ A glass has 0.500 J of gravitational potential energy when sitting on a shelf with a height of 0.400 m. What is the mass of the glass?

a) 0.127 kg

b) 1.25 kg

c) 3.92 kg

d) 0.200 kg

__9.__ An apple has 0.800 J of gravitational potential energy when hanging from a tree. If it falls off the branch, how much gravitational potential energy will it have when it has fallen half the distance to the ground?

a) 1.60 J

b) 0.400 J

c) 3.92 J

d) 0 J

__10.__ A net force of 5.00 newtons is used to displace a 3.00 kg box a distance of 4.00 m in 2.00 second. How much work is done on the box?

a) 6.00 J

b) 8.00 J

c) 15.0 J

d) 20.0 J

__11.__ A net force of 6.00 N is used to move a box 5.00 m in 2.00 s. How much power is used?

a) 1.20 W

b) 12.0 W

c) 13.0 W

d) 15.0 W

__12.__ The motor of a snowmobile has an output of 1.00 kW. If the motor applies a force of 650 N to move the snowmobile at constant speed, what is the magnitude of the velocity of the snowmobile?

a) 1.5 m/s

b) 650 m/s

c) 6.5 × 10^{5} m/s

d) 3.0 m/s

__13.__ Two skaters with masses of 55.0 kg and 85.0 kg, respectively, face each other on the ice. They are initially at rest, but they push off each other in such a way that they move away from each other in opposite directions. If the speed of the lighter skater after they push off is 3.50 m/s, what is the speed of the 85.0 kg skater?

a) 5.41 m/s

b) 2.26 m/s

c) 8.57 m/s

d) 1.21 m/s

__14.__ A worker exerts 45 W of power while lifting a 10.0 N box to a height of 1.0 m. How long does this take?

a) 35 s

b) 4.5 s

c) 0.22 s

d) 0.02 s

**Part III—Calculations**

Perform each of the following calculations.

__15.__ At what height would a 5.5 kg bowling ball have 30.0 J of gravitational kinetic energy? (Assume g = 9.81 m/s^{2}.)

__16.__ At what speed (the magnitude of the velocity) would a truck with a mass of 1.1 × 10^{4} kg have a kinetic energy of 5.0 × 10^{4} J?

__17.__ A compressed spring with a constant of 38 N/m has 5.90 J of elastic potential energy. How far has it been compressed from its equilibrium position?

__18.__ A girl does 48 J of work pushing her bicycle with a steady force of 15.0 N in the direction of its motion. How far does the bicycle move during this time?

__19.__ Calculate the magnitude of the momentum of a football player with a mass of 140 kg and a velocity of 5.0 m/s.

__20.__ A tennis player exerts a force of 35 N for a period of 0.15 s on a tennis ball with a mass of 0.10 kg. Calculate the change in the velocity of the tennis ball.