ikram (ai2734) – hw1013 – Swinney – (58785)
1
This
printout
should
have
9
questions.
Multiplechoice questions may continue on
the next column or page – find all choices
before answering.
001
(part 1 of 2) 10.0 points
A small air compressor operates on a 2
.
7 hp
(horsepower) electric motor for 9
.
6 hours a
day.
How much energy is consumed by the motor
daily? 1 hp equals about 750 watts.
Correct answer: 6
.
9984
×
10
7
J.
Explanation:
Let :
P
= 2
.
7 hp
,
and
t
= 9
.
6 h
.
P
= 2
.
7 hp
·
750 W
hp
= 2025 W = 2025 J
/
s
,
so
W
=
P t
= (2025 J
/
s) (9
.
6 h)
·
3600 s
1 h
=
6
.
9984
×
10
7
J
.
002
(part 2 of 2) 10.0 points
If electricity costs 12 cents per kilowatthour,
how much does it cost to run the compressor
each day?
Correct answer: 233
.
28 cents.
Explanation:
The energy in kilowatthours is given by:
E
=
P t
= (2
.
025 kW) (9
.
6 h)
= 19
.
44 kW
·
h
,
Cost = (19
.
44 kW
·
h) (12 cents
/
kW
·
h)
=
233
.
28 cents
.
At
12
cents
per
kW
·
h,
it
would
cost
233
.
28 cents to run the compressor for a day.
keywords:
003
10.0 points
When a rattlesnake strikes, its head acceler
ates from rest to a speed of 20 m
/
s in 0
.
33 s
seconds. Assume for simplicity that the only
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 Spring '07
 Swinney
 mechanics, Energy, Mass, Potential Energy, Correct Answer, Gravitational forces

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