Name___________________________________
ENERGY, WORK, and POWER - P. 257
Physics Classwork 04/18/17
PH.19, 20, 21
1) A weightlifter raises a 160. kg barbell to a height of 1.90 m. How much work is done by the
weightlifter in lifting the barbell?
1)
2) A 2.00 kg female great horned owl (Bubo virginianus) silently swoops directly from a
branch 12.8 m high in a tree to capture an unfortunate field mouse (Apodemus sylvaticus) on
the ground, a 27.0 m distance from the owl's perch. Calculate the work done by gravity on
the owl during its downward flight.
2)
3) If a measurement is given in centimeters, what do you have to do before you can calculate the amount of work
done?
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4) Chuck weighs 560 N on a bathroom scale containing a heavy spring. The spring is
compressed 2.5 cm under his weight. Find the total work done on the spring during the
compression.
4)
5) After scoring a touchdown, a(n) 74.0 kg wide receiver celebrates by leaping 128 cm off the
ground. How much work was done in the celebration?
5)
6) In order for work to be done, at least part of the force must be ___________________ to the direction of motion.
7) A wagon is pulled by a force of 40.0 N on the handle at an angle of 40.0° with the
horizontal. If the wagon is pulled once around a circle of radius 30.0 m, how much work is
done?
7)
8) A lawn mower is pushed by a force of 78.0 N on the handle that makes an angle of 40..0°
with the horizontal. How much work is done in pushing the mower 1.10 km in mowing the
yard?
8)
9) A woman pushes on a baby stroller at an angle of 60.0° below the horizontal. If she does
500. J of work on the stroller while it moves 24.0 m, how much force does she exert?
9)
10) ______ is the work done per unit of time.
10)
11) Distinguish between work and power.
Work is ________________________________________________________________________________.
Power is _______________________________________________________________________________.
12) Lifting a box of twenty books and lifting each of the twenty books one at a time requires the same
amount of power.
13) The SI unit of power is the ______.
13)
T or F
14) One watt is equal to _____.
A) one second times one joule
C) one meter per second
14)
B) one meter times one joule per second
D) one joule per second.
15) Which of the following is NOT one of the equations which can be used to calculate the amount of
power?
mgh
FxD
W
W
A) P =
B) P =
C) P =
D) P =
T
T
T
FxT
15)
16) Two students are moving 80.-N cartons of books from the floor onto a platform. Student 1 moves 12 cartons in
7.0 minutes. Student 2 moves the same number of cartons in 5.0 minutes. Which student does more work?
Explain your answer.
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Which student exerts more power? Explain.
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17) An engine that can do 6600 joules in twenty seconds has more power than an engine that can do 120,000
joules of work in six minutes.
18) An elevator lifts a total mass of 1.40 x 103 kg a distance of 44.0 m in 13.3 sec. How much
power does the elevator demonstrate?
18)
19) At what speed can a 140-W motor lift a 2600-N load?
19)
20) A cyclist exerts a force of 14.0 N in riding a bike 291 m in 38.0 sec. What is the cyclist's
power?
20)
21) What power does a pump develop to lift 38 L of water per minute from a depth of 110 m?
(A liter of water has a mass of 1.00 kg.)
21)
22) How much power is generated by a student with a mass of 60. kg who runs up a flight of
steps 3.0 m high in 1.96 s?
22)
23) A 2.00 x 103 kg block of granite is lifted from the bottom of a quarry to the top at a constant
velocity. The quarry is 176 m deep.
a. How much work was done to the granite block?
b. What is the change in potential energy of the block?
c. If the lift took 70.0 s, how much power was expended?
23) a.
b.
c.
T or F