Question

A string is wound round the rim of a mounted flywheel of mass 20 kg and radius 20 cm. A steady pull of 25 N is applied on the cord. Neglecting friction and mass of the string, the angular acceleration of the wheel is

• A. 50 $\,s^{-2}$
• B. 25 $\,s^{-2}$
• C. 12.5 $\,s^{-2}$
• D. 6.25 $\,s^{-2}$

Answer 1

Answer: (C)

The mass of flywheel = 20 kg
Radius = 20 cm
= $\frac{20}{100} m = \frac{1}{5}m$
The moment of inertia = $\frac{1}{2}MR^2 = \frac{1}{2} \times 20 \times \frac{1}{5}$
I = 0.4 $kg-m^2$
Angular acceleration $\alpha = \frac{\tau}{I} $
= $\frac{FR}{I} = \frac{25 \times \frac{1}{5}}{0.4} =12.5 s^{-2}$