Question

Moment of inertia of a body about an axis is $4\, kg - m ^{2}$. The body is initially at rest and a torque of $8\, N-m$ starts acting on it along the same axis. Work done by the torque in $20\, s$, in joules, is

• A. 40
• B. 640
• C. 2560
• D. 3200

Answer 1

Answer: (D)

Given, $l=4\, kg - m ^{2}, \tau=8\, N - m$ and $t=20\, s$
$\tau=l \alpha$
$\Rightarrow \alpha=\frac{\tau}{l}=\frac{8}{4}=2$
$\theta=\frac{1}{2} \alpha t^{2}$
$\Rightarrow \theta=\frac{1}{2} \times 2 \times 20 \times 20=400$
$\omega=\tau \theta=8 \times 400=3200\, J$