Question

A wheel rotating at an angular speed of 20 rad$s^{-1}$, is brought to rest by a constant torque in 4s.If the M.I is 0.2 kg $m^2$, the work done in first 2s is:

• A. $50J$
• B. $30J$
• C. $20J$
• D. $10J$

Answer 1

The correct option is A $50J$

Angular acceleration$\alpha =\frac{20}{4}=5$

Torque=$I\alpha =5\times 0.2=1$

Angular displacement in first 2 secs=$20\times 2+\frac{1}{2}5\times 2^2=50$

Work done=Torque×angular displacement$=1\times 50=50J$