Question

A wheel having angular momentum $2 \pi kg - m ^2 / s$ about its vertical axis, rotates at the rate of $60\, rpm$ about this axis, The torque which can stop the wheel's rotation in $30 \sec$ would be

• A. $\frac{\pi}{18} Nm$
• B. $\frac{2 \pi}{15} Nm$
• C. $\frac{\pi}{12} Nm$
• D. $\frac{\pi}{15} Nm$

Answer 1

Answer: (D)

$\tau \times \Delta t = L _0 $
$\left\{\because \text{since} L _f=0\right\}$
or $\tau \times 30=2 \pi$
$\tau=\frac{\pi}{15} N - m$