Question

If there is change of angular momentum from $J$ to $5\, J$ in $5\, s$, 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., $\frac{d J}{d t}=\tau$
Given, $J_{1}=J,\, J_{2}=5 J$
$\therefore \Delta J=J_{2}-J_{1}=5 J-J=4\, J$
Hence, $\tau=\frac{4}{5} J$