Mass A (7 kg) and mass B (8 kg) sit on the ground, 4 m apart. a.) What is size o
ID: 1338742 • Letter: M
Question
Mass A (7 kg) and mass B (8 kg) sit on the ground, 4 m apart.
a.) What is size of the the gravitational force:
on A from B? N
on B from A? N
b.) What is the size of the gravitational force:
on A from the Earth? N
on B from the Earth? N
c.) Examining your results from above, explain why we normally only worry about the gravitational force on such objects from the Earth, and don't worry about including the gravitational force on objects from each other.
The forces that A and B exert back on the Earth itself are ---Select---(same size, smaller, larger, or n/a these dont exert a force on earth) the same size as smaller than larger than n/a - these objects do not exert forces on the Earth those you found in part b, respectively.
Explanation / Answer
Gravitaional force, F = GmAmB/r2
G = 6.67408 × 10-11 m3 kg-1 s-2.
mA = 7 kg.
mB = 8 kg.
r = 4 m.
Substituting,
F = [6.67408 × 10-11 x 7 x 8] / 16 = 23.36 x 10-11 N
Force on A from B = Force on B from A = 23.36 x 10-11 N
b)
Force on A from earth = FA = GMmA/R2
M = mass of earth = 5.972 × 1024 kg
R = radius of earth = 6,371 km = 6.37 x 106 m.
FA = [6.67408 × 10-11 x 5.972 × 1024 x 7] / 40.5769 x 1012 = 68.76 N
Similarly,
FB = GMmB/R2
FB = [6.67408 × 10-11 x 5.972 × 1024 x 8] / 40.5769 x 1012 = 78.58 N
c)
Compared to earth's gravitational force, the force between two objects are negligible (around 1/1010 tims smaller)
So we can neglect forces between two objects.