Q.

The acceleration due to gravity at a height 1 km above the earth is the same as at a depth d below the surface of earth. Then      [2017]
 

1 d=1 km  
2 d=32 km  
3 d=2 km  
4 d=12 km  

Ans.

(3)

The acceleration due to gravity at a height h is given as

         gh=g(1-2hRe)

where Re is the radius of the Earth.

The acceleration due to gravity at a depth d is given as

        gd=g(1-dRe)

Given,  gh=gd

  g(1-2hRe)=g(1-dRe)

or    d=2h=2×1=2km                                    (h=1km)