Question

If there is change of angular momentum from $J$ to $5J$ in $5s$, then the torque is :

• A. $\frac{\text{3J}}{\text{5}}$
• B. $\frac{\text{4J}}{\text{5}}$
• C. $\frac{\text{5J}}{4}$
• D. None of these

Answer 1

Answer: (B)

Torque is defined as rate of change of angular momentum.
We know that rate of change of angular momentum (J) of a body is equal to the external torque $(\tau )$ acting upon the body.
i.e., $\frac{dJ}{dt}=\tau$
Given, $J_1=J,J_2=5J$
$\therefore \Delta J=J_2-J_1=5J-J=4J$
Hence, $\tau =\frac{4}{5}J$