Download Chapter 4 Test.final A

A
SPH3U
November 24, 2010
Name:______________________________________________
Chapter 4: Work and Energy
Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
____
1. A person lifts a pail of water of mass of 1.50 kg from the ground to a deck, 1.00 m above the ground. How
much work was done by gravitational force on the pail of water?
a. –14.7 J
d. +0.153 J
b. +1.50 J
e. +14.7 J
c. –1.50 J
____
2. In which case is negative work done?
a. The work done by Earth on a ball as the ball, which was initially at rest, falls 3.0 m down
towards Earth.
b. A eastward force is applied to an eastward moving soccer ball that is already moving at a
constant velocity to increase its speed in that direction.
c. A cart is moving at a constant velocity of 10 m/s [W] when a 0.5 N [downward] force is
applied.
d. The work done by Earth on an arrow as it is fired 200 m straight up into the air.
e. Earth applies a force on the Moon as the Moon travels one completion rotation in orbit
around Earth.
____
3. A construction worker does 450 J of work in lifting a load of bricks from the ground to a support stand 1.50 m
from the ground. What was the mass of the bricks she lifted?
a. 300 kg
d. 0.327 kg
b. 3.06 kg
e. 30.6 kg
c. 68.9 kg
____
4. A 5.00-kg sack of potatoes is raised to a height of 2.00 m and then thrown at a constant velocity of 2.00 m/s
onto a truck. What is the kinetic energy of the potatoes?
a. 5.00 J
d. 103 J
b. 98.0 J
e. 108 J
c. 10.0 J
____
5. At a height of 3.00 m above the ground, a 0.500-kg ball is thrown with an initial speed of 30.0 m/s in an arc
from point A to point C. When the ball is 6.00 m above the ground travelling upward, the speed of the ball is
a. 30.0 m/s
d. 26.9 m/s
b. 7.67 m/s
e. 29.0 m/s
c. 6.76 m/s
____
6. A 15-kg load of groceries is lifted up from the ground to the fifth floor of an apartment building. Each floor is
5.00 m high. The potential energy of the groceries with respect to the second floor is
a. 3.68  103 J
d. 2.20  103 J
3
b. 2.94  10 J
e. 3.0  100 J
c. 7.5  101 J
1
____
7. A cheerleader is thrown vertically upward into the air. As the cheerleader rises, which one of the following
quantities increases?
a. gravitational potential energy
d. acceleration
b. speed
e. mechanical energy
c. kinetic energy
____
8. An elevator motor lifts a load of 2500 kg a height of 12.0 m in 3.00 seconds. The energy required by the
motor to accomplish this task is 300 000 J. What is the efficiency of the elevator?
a. 10.0%
d. 102%
b. 98.0%
e. 8.17%
c. 30.0%
____
9. If two substances of equal mass are supplied the same amount of thermal energy and their final temperatures
are different, you can assume that they have
a. different heat capacities
d. different densities
b. the same volume
e. different volumes
c. different abilities to conduct heat
____ 10. How much heat is required to raise the temperature of 40 g of water 20°C?
(cw = 4.18  103 J/kg·°C)
a. 5.2 J
d. 3.3  105 J
3
b. 3.3  10 J
e. 2.1  106 J
c. 8.0  10–1 J
____ 11. The specific heat capacity of iron is 4.5  102 J/kg·C. The heat energy required to heat 5.0 kg of iron from
10C to 40C is
a. 9.0  104 J
d. 2.2  104 J
4
b. 6.8  10 J
e. 7.5  101 J
0
c. 3.0  10 J
____ 12. A liquid is being heated on a hotplate. The transfer of heat in the liquid through a circular path is called
a. radiation
d. conduction
b. convection
e. heat exchange
c. heat transfer
____ 13. A 100-kg person has an average power output of 140 W while walking up a 0.50-km high mountain. How
long does it take the person to climb the mountain?
a. 9.7  10–1 h
d. 3.6  102 h
–1
b. 7.1  10 h
e. 1.4  100 h
c. 5.8  101 h
____ 14. The amount of work an 118-W electric mower can do in 3.0 min is
a. 3.5  102 J
d. 2.1  104 J
b. 1.5  100 J
e. 3.9  101 J
–2
c. 2.5  10 J
____ 15. A motorboat has a power output of 3.2  107 W and provides 4.0  106 J of energy in
a. 1.2 10–1 min
d. 8.0  10–1 h
b. 8.0  101 min
e. 8.0  101 s
–1
c. 1.2  10 s
2
Short Answer
16. What is the difference between positive and negative work?
17. Analyze the sketches below and decide which hair dryer has the greater power rating. Explain your choice.
Problem
18. A 2.0-kg bag is held by a string to the ceiling as shown in the diagram below. A 10-g bullet travelling at 100
m/s strikes the stationary bag. The speed of the bag after the collision is 0.80 m/s. Assuming there is no
friction, determine the maximum height, in centimetres, of the bag after the collision.
3
19. A person uses a rope and pulley to lift a 75-kg sack 2.0 m onto a truck. The downward force on the rope over
the 2.0 m distance is 2.5  103 N.
(a) Calculate the work done in raising the sack.
(b) How much useful work was done?
(c) What is the efficiency of the rope and pulley in raising the sack onto the truck?
20. A 500 g piece of silver at 150C is submerged in 1000 g of water at 5C to be cooled. Determine the final
temperature of the silver and water given
cwater = 4.18  103 J/kg·C
csilver = 2.4  102 J/kg·C
21. An elevator motor provides 45.0 kW of power while lifting a 2000-kg elevator 35.0 m. If the elevator
contains six passengers of the same mass and it takes 20.0 s to accomplish this task, determine the mass of
each passenger.
4
Work and Energy
Answer Section
MULTIPLE CHOICE
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
A
D
E
C
E
A
A
B
A
B
B
B
A
D
C
REF:
REF:
REF:
REF:
REF:
REF:
REF:
REF:
REF:
REF:
REF:
REF:
REF:
REF:
REF:
K/U
K/U
K/U
K/U
K/U
K/U
K/U
K/U
K/U
K/U
K/U
K/U
K/U
K/U
K/U
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
OBJ:
4.2
4.2
4.2
4.3
4.4
4.3
4.3
4.4
4.5
4.5
4.5
4.5
4.6
4.6
4.6
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
LOC:
EW1.02
EW1.01, EW1.02
EW1.02
EW1.01, EW1.03
EW1.03
EW1.03
EW1.01, EW1.03
EW1.05
EW1.01, EW1.03
EW1.01, EW1.03
EW1.03
EW1.01
EW1.04
EW1.04
EW1.04
SHORT ANSWER
16. ANS:
When positive work is done the force applied is in the same direction of the object's displacement, whereas
when negative work is done the force is applied in the opposite direction of the object's displacement.
REF: K/U
OBJ: 4.2
LOC: EW1.01, EW1.02
17. ANS:
Modern pole vaulting poles are stronger, have a lower density, and are stiffer. (The student may choose any
two.) This results in more energy being used in lifting the vaulter and not lost to the twisting or bending of the
pole. More of the elastic energy is returned to the pole vaulter and, thus, the athlete is lifted higher.
REF:
MC
OBJ: 4.4
LOC: EW1.05, EW3.02
PROBLEM
18. ANS:
mass of bag (M) = 2.0 kg
mass of bullet (m) = 10 g = 0.010 kg
speed of bag before collision (V) = 0 m/s
speed of bag after collision (V') = 0.80 m/s
speed of bullet before collision (v) = 100 m/s
speed of bullet after collision (v') = 0 m/s
height of bag after collision (h) = ?
5
The maximum height of the bag after the collision was 3.3 cm.
REF: K/U
19. ANS:
m = 75 kg
d = 2.0 m
F = 2.5  103 N
OBJ: 4.4
LOC: EW1.03
(a)
The work done in raising the sack is 5.0  103 J.
(b)
The useful work was 1.5  103 J.
6
(c)
The efficiency of the rope and pulley in raising the sack onto the truck was 30%.
REF: K/U
OBJ: 4.4
20. ANS:
ms = 500 g = 0.50 kg
mw = 1000 g = 1.0 kg
cw = 4.18  103 J/kg·C
cs = 2.4  102 J/kg·C

final temperature = tf
ts = 150C – tf
tw = tf – 5C
LOC: EW1.05
The final temperature of the silver and water is 9.0C.
REF: K/U
OBJ: 4.5
21. ANS:
P = 45.0 kW = 4.5  104 W
mass of elevator (m1)= 2.00  103 kg
h = 35.0 m
t = 20.0 s
number of passengers = 6
mass of elevator and passengers (M) = ?
mass of each passenger (m2) = ?
LOC: EW1.03
Ep = Mgh
7
The mass of each passenger on the elevator was 1.03  102 kg.
REF:
K/U
OBJ: 4.6
LOC: EW1.04
8