Question

What torque will increase angular velocity of a solid disc of mass $16kg$ and diameter $1m$ from zero to $2$rpm in $8s$?

• A. $\frac{\pi }{4}N-m$
• B. $\frac{\pi }{2}N-m$
• C. $\frac{\pi }{3}N-m$
• D. $\pi N-m$

Answer 1

The correct option is D $\pi N-m$

Torque $\left(\tau \right)=I\alpha$
$\tau =\frac{1}{2}\times M{R}^2\times \frac{2\pi (n_2-n_1)}{t}$
$\therefore$ $\tau =16\times {\left(\frac{1}{2}\right)}^2\times \pi \frac{(2-0)}{8}=\pi N-m$