A body weighs 72 N on the surface of the earth. What is the gravitational force on it due to earth at a height equal to half the radius of the earth from the surface

Options

A. 20 N
B. 45 N
C. 40 N
D. 90 N

Answer

A

Explanation

Weight of the body at the surface of the earth `=mg =45 N`
using `g =(g)/(1+(h)/(R ))^(2) rarr mg =(mg)/(1+(R )/(2R))^(2)`
`w=(45)/(1+1/2)^(2)=(4xx45)/(9)=20 N`