Question

A body weighs $36\text{N}$ at a depth equal to half of earth radius. The weight of the body on surface of earth will be

• A. $36\text{N}$
• B. $18\text{N}$
• C. $54\text{N}$
• D. $72\text{N}$

Answer 1

The correct option is D $72\text{N}$

Variation of acceleration due to gravity with depth $d$ is given by

$g^{{}^{\prime }}=g(1-\frac{d}{R})$; for $d=\frac{R}{2}$

$=g(1-\frac{R}{2R})=\frac{g}{2}$

$\Rightarrow g=2g^{{}^{\prime }}$

$\therefore mg=2m{g}^{{}^{\prime }}=2\times 36=72\text{N}$