Chapter 12
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Mr. Newton, whose mass is 60.0 kg, is doing a
physics demonstration in the front of the
classroom.
A) how much gravitational force does he exert
on 55.0 kg Martha in the front row, 1.50 m
away?
F = G*m1*m2
d2
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G = 6.67x10-11Nm2/kg2
m1 = 60.0 kg
m2 = 55.0 kg
d = 1.50 m
F=?
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F = (6.67x10-11Nm2/kg2)(60.0kg)(55.0kg)
(1.50m)2
F = 9.78x10-8 N
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B) how does this compare to what he exerts on
65.0 kg Lester, 4.00 m away in the back row?
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G = 6.67x10-11Nm2/kg2
m1 = 60.0 kg
m2 = 65.0 kg
d = 4.00 m
F=?
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F = (6.67x10-11Nm2/kg2)(60.0kg)(65.0kg)
(4.00m)2
F = 1.63x10-8 N
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Our galaxy, the Milky Way, contains
approximately 4.0x1011 stars with an average
mass of 2.0x1030 kg each. How far away is the
Milky Way from out nearest neighbor, the
Andromeda Galaxy, if Andromeda has an
average mass of 8x1041 kg and attracts the
Milky Way with a gravitational force of
2.4x1030 N?
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G = 6.67x10-11Nm2/kg2
m1 = (2.0x1030kg)(4.0x1011) = 8x1041 kg
m2 = 8x1041 kg
F = 2.4x1030 N
d=?
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d = √G*m1*m2/F
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d= √(6.67x10-11)(8x1041)(8x1041)/(2.4x1030)
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d = 4.2x1021m
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Force= mass * acceleration (gravity)
m * g = G * m 1 * m2
d2
One of the masses cancels, left with
g = G * m2
d2
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Teresa is standing in the lunch line 6.38x106m
from the center of Earth. Earth’s mass is
5.98x1024kg.
What is the acceleration due to gravity?
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m2=5.98x1024 kg
d=6.38x106m
G=6.67x10-11N*m2/kg2
g=?
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g = G * m2
d2
g = (6.67x10-11)(5.98x1024)
(6.38x106)2
g = 9.80 m/s2