Question

The angular momentum of a rotating body changes from $A_0$ to $4A_0$ in 4 seconds. The torque acting on the body is :

• A. $\frac{3}{4}{A}_0$
• B. $4A_0$
• C. $3A_0$
• D. $\frac{3}{2}{A}_0$

Answer 1

Answer: (A)

$\frac{3}{4}{A}_0$

The torque is basically the first derivative of angular momentum w.r.t time.
$\tau =\frac{dL}{dt}$
In this case just the final angular momentum, initial angular momentum and the time interval between them are given.
Thus we calculate $\tau$ as $\frac{4A_0-A_0}{4}=\frac{3A_0}{4}$