adamkiewicz (ja28724) – Energy of a system – Morozova – (11102)
1
This
printout
should
have
12
questions.
Multiplechoice questions may continue on
the next column or page – find all choices
before answering.
001
10.0 points
This question is typical on some driver’s li
cense exams: A car moving at 43 km
/
h skids
13 m with locked brakes.
How far will the car skid with locked brakes
at 107
.
5 km
/
h?
Correct answer: 81
.
25 m.
Explanation:
107
.
5 km
/
h
43 km
/
h
= 2
.
5
At 2
.
5 times the speed, it has 6
.
25 times the
KE
parenleftbigg
1
2
m v
2
parenrightbigg
and will skid 6
.
25 times as far:
81
.
25 m.
Since the frictional force is about
the same in both cases, the distance has to
be 6
.
25 times as great for 6
.
25 times as much
work done by the pavement on the car.
002
10.0 points
The Joule and the kilowatthour are both
units of energy.
11
.
9 kW
·
h
is equivalent to how
many
Joules?
Correct answer: 4
.
284
×
10
7
J.
Explanation:
1 W = 1 J
/
s
11
.
9 kW
·
h = (11
.
9 kW
·
h)
·
1000 W
kW
·
3600 s
1 h
= 4
.
284
×
10
7
W
·
s
=
4
.
284
×
10
7
J
.
003
(part 1 of 5) 10.0 points
A 18
.
9 kg block is dragged over a rough, hor
izontal surface by a constant force of 118 N
acting at an angle of angle 31
◦
above the hor
izontal.
The block is displaced 48
.
2 m, and
the coefficient of kinetic friction is 0
.
203.
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 Spring '08
 moro
 Physics, Energy, Force, Friction, Correct Answer, 118 N force

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