A bar magnet is osciallating in the earth's magnetic field with a period T. What happens to its period of motion of its mass is quad-rupled without changing its dimensions?

Options

A. Motion remains SHM with period `=T//2`
B. Motion remains SHM with period `=2T`
C. Motion remains SHM with period `=4T`
D. Motion is not SHM, but period `=T`

Answer

B

Explanation

`T=2pisqrt(I//MH)`
where I=moment of inertia of magnet about the suspension fibre `=mass((l^2+b^2))/(12)`
when mass is quadrupled. I becomes 4 times. Therefore, T becomes `sqrt4` times i.e. `2T` the motion continues to be simple harmonic.