schneiter (tcs639) – HW19 – Ross – (89152)
1
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printout
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have
7
questions.
Multiplechoice questions may continue on
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before answering.
001
10.0 points
Tom has a mass of 72
.
9 kg and Sally has a
mass of 41
.
8 kg. Tom and Sally are standing
39
.
4 m apart on a massless dance floor. Sally
looks up and she sees Tom.
She feels an
attraction.
If the attraction is gravitation, find its mag
nitude.
Assume both can be replaced by
spherical masses and that the gravitational
constant is 6
.
67259
×
10
−
11
N
·
m
2
/
kg
2
.
Correct answer: 1
.
3098
×
10
−
10
N.
Explanation:
Let :
m
T
= 72
.
9 kg
,
m
S
= 41
.
8 kg
,
d
= 39
.
4 m
,
and
G
= 6
.
67259
×
10
−
11
N
·
m
2
/
kg
2
.
By Newton’s universal law of gravitation,
F
=
G
m
T
m
S
d
2
= (6
.
67259
×
10
−
11
N
·
m
2
/
kg
2
)
×
(72
.
9 kg) (41
.
8 kg)
(39
.
4 m)
2
=
1
.
3098
×
10
−
10
N
.
002
10.0 points
How high does a rocket have to go above the
Earth’s surface so that its weight is reduced
to 56
.
5 % of its weight at the Earth’s sur
face?
The radius of the Earth is 6380 km
and the universal gravitational constant is
6
.
67
×
10
−
11
N
·
m
2
/
kg
2
.
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 Spring '08
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 mechanics, Mass, General Relativity, kg

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