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Question


A body weighs 72 N on the surface of the Earth. What will be the force of gravity acting on the body at a height equal to half the radius of the Earth above the Earth's surface?


Options:
A .   32 N
B .   20 N
C .   10 N
D .   0 N
Answer: Option A
:
A
Weight of the body at earth's surface is:
We=GMmR2      .......(1)
where, G-universal gravitational constant, M-mass of earth and R-radius of earth, m- Mass of the body
Weight of the body at a height h above the earth's surface is given by
We=GMm(R+h)2
According to the question, h=R2
We=GMm(R+R2)2 
We=4GMm9R2  ....(2)
Dividing equation (2) by equation(1), we get
WeWe=4GMm/9R2GMm/R2
WeWe=49
Given weight on earth's surface is,  We=72 N
We72=49
We=32 N

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