A uniform metallic rod rotates about its perpendicular bisector with constant angualr speed. If it is heated uniformly to raise its temperature slightly, then

Options

A. Its speed of rotation increases
B. Its speed of rotation decreases
C. Its speed of rotation remains same
D. Its speed increases because its moment of inertia increases

Answer

B

Explanation

When the rod is heated, it expands. No external torque is acting on the system so angular momentum should be conserved.

L = Angular momentum = `I omega `= constant
`rArr I_(1) omega_(1) = I_(2) omega_2`
Due to expansion of the rod `I_(2) gt I_(1)`
`rArr (omega_2)/(omega_1) (I_1)/(I_2) lt 1 rArr omega_2 lt omega_1`
So, angular velocity (speed of rotation) decreases.