CGPET 2015 Solved Paper

Suppose depth inside the earth is h.
As we know that, inside the earth
gi∞(

R−h

R3

) ....(i)
On the surface of the earth
gs∞

1

R2

....(ii)
From Eqs.(i) and (ii), we get

gi

gs

=

(R−h)R2

R3

=

R−h

R

⇒

1

4

=

R−h

R

⇒R=4R−4h
⇒3R=4h
⇒h=

3

4

R.