Compare the weight of a body 100 km above and 100 km below the surface of the earth . Radius of the earth = 6400 km .

Options

A. 60m
B. 80m
C. 100m
D. 120m

Answer

C

Explanation

For earth, `g = (GM)/(R^2) = 4/3 pi R rho G`
where M and R are the mass and radius of the earth respectively. For the planet, g. `= (GM.)/(R.^2) = 4/3 pi R. rho G`
where M. and R. are the mass and radius of the planet respectively.
` therefore (g)/(g.) =( R)/(R.) = 6400/320 = 20`
Let h and h. be the heights upto which the man can jump on surface of the earth and planet respectively. Then
mgh = mg.h. or `h. = (g)/(g.) h = 20 xx 5 =100 m`