Question

A wheel of mass of inertia = 20 kgm² moves from rest to 120rpm in 20 sec. How large torque acts on it in N. m.​

Answer 1

Answer:

$120 \: rpm \\ \\ = 120 \times 2\pi \times \frac{1}{60} \: radian \: per \: s \\ = 4\pi \: \: \frac{rad}{s}$

Now calculate angular acceleration

$\alpha = \frac{4\pi - 0}{20} = \frac{\pi}{5} \: \frac{rad}{ {s}^{2} }$

Now use

$\tau = I \alpha = 20 \times \frac{\pi}{5} = 4\pi \: Nm$