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homework 18 – PAPAGEORGE, MATT – Due: Mar 1 2008, 4:00 am
1
Question 1, chap 8, sect 5.
part 1 of 1
10 points
A hot rod of mass 1300 kg, starting from
rest reaches a speed of 180 m
/
s in only 28
.
4 s.
What is the average output power?
1.
0
.
000145061 MW
2.
1
.
4831 MW
3.
0
.
0261109 MW
4.
0
.
00823944 MW
5.
0
.
741549 MW
correct
Explanation:
The average output power is equal to the
kinetic energy acquired divided by the total
time, so
P
=
1
2
mv
2
t
=
1
2
(1300 kg) (180 m
/
s)
2
28
.
4 s
·
mW
10
6
W
= 0
.
741549 MW
Question 2, chap 8, sect 5.
part 1 of 1
10 points
A car with a mass of 1
.
30
×
10
3
kg starts
from rest and accelerates to a speed of 12.3
m/s in 14.1 s.
Assume that the force of
resistance remains constant at 492.2 N during
this time.
What is the average power developed by
the car’s engine?
Correct answer: 10001
.
4 W (tolerance
±
1
%).
Explanation:
Basic Concepts:
v
f
=
a
Δ
t
and
Δ
x
=
1
2
a
(Δ
t
)
2
since
v
i
= 0 m/s.
P
=
W
Δ
t
=
F
Δ
x
Δ
t
F
=
ma
+
F
r
Given:
m
= 1
.
30
×
10
3
kg
v
f
= 12
.
3 m
/
s
Δ
t
= 14
.
1 s
F
r
= 492
.
2 N
Solution:
a
=
v
f
Δ
t
so
P
=
F
Δ
x
Δ
t
=
F
·
1
2
a
(Δ
t
)
2
Δ
t
=
Fa
Δ
t
2
=
(
ma
+
F
r
)
v
f
2
=
p
m
v
f
Δ
t
+
F
r
P
·
v
f
2
=
b
(1300 kg)(12
.
3 m
/
s)
14
.
1 s
+ 492
.
2 N
B
·
12
.
3 m
/
s
2
= 10001
.
4 W
Question 3, chap 8, sect 5.
part 1 of 1
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 Spring '09
 KLEINMAN
 Physics, Mass, Power, Work

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