Question

A tunnel has been dug through the centre of the earth, and a ball is released in it. It executes S.H.M. with time period

• A. $42\text{minutes}$
• B. $1\text{day}$
• C. $1\text{hour}$
• D. $84.6\text{minutes}$

Answer 1

The correct option is D $84.6\text{minutes}$

Radius of earth $=6400\text{km}$
Since, Time period, $T=2\pi \sqrt{\frac{R}{g}}$
$\therefore T=2\pi \sqrt{\frac{6400\times 1000}{10}}$
$=2\pi \times 800$$=1600\pi \text{s}$
$=84.6\text{minutes}$