alexander (jra2623) – homework 14 – Turner – (92510)
1
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printout
should
have
12
questions.
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before answering.
001
10.0 points
A hot rod of mass 1700 kg, starting from rest
reaches a speed of 120 m
/
s in only 11
.
8 s.
What is the average output power?
1.
0
.
0879058 MW
2.
0
.
000732548 MW
3.
0
.
0172881 MW
4.
1
.
03729 MW
correct
5.
2
.
07458 MW
Explanation:
The average output power is equal to the
kinetic energy acquired divided by the total
time, so
P
=
1
2
mv
2
t
=
(1700 kg) (120 m
/
s)
2
2 (11
.
8 s)
·
mW
10
6
W
= 1
.
03729 MW
002
10.0 points
A car with a mass of 1
.
67
×
10
3
kg starts from
rest and accelerates to a speed of 11.8 m/s in
17.9 s.
Assume that the force of resistance
remains constant at 337.8 N during this time.
What is the average power developed by
the car’s engine?
Correct answer: 8488
.
29 W.
Explanation:
Let :
m
= 1
.
67
×
10
3
kg
,
v
f
= 11
.
8 m
/
s
,
Δ
t
= 17
.
9 s
,
and
F
r
= 337
.
8 N
.
v
f
=
a
Δ
t
and Δ
x
=
1
2
a
(Δ
t
)
2
since
v
i
= 0
m/s, and
F
=
m a
+
F
r
, so
P
=
F
Δ
x
Δ
t
=
F
·
1
2
a
(Δ
t
)
2
Δ
t
=
F a
Δ
t
2
=
(
m a
+
F
r
)
v
f
2
=
parenleftBig
m
v
f
Δ
t
+
F
r
parenrightBig
·
v
f
2
=
bracketleftbigg
(1670 kg)(11
.
8 m
/
s)
17
.
9 s
+ 337
.
8 N
bracketrightbigg
×
11
.
8 m
/
s
2
=
8488
.
29 W
.
003
10.0 points
A car weighing 8900 N moves along a level
highway with a speed of 77 km
/
h. The power
of the engine at this speed is 71 kW. The car
encounters a hill inclined at an angle of 8
.
8
◦
with respect to the horizontal.
If there is no change in the power of the
engine, and no change in the resistive forces
acting on the car, what is the new speed of
the car on the hill?
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 Summer '08
 Kaplunovsky
 Force, Kinetic Energy, Mass, Potential Energy, Work, Alexander

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