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 $=\frac{1}{2} M R^{2}$
$=\frac{1}{2} \times 20 \times\left[\frac{1}{5}\right]^{2}$
$I<0.4\, kg \cdot m ^{2}$
Angular acceleration $\alpha =\frac{\tau}{I}$
$=\frac{F R}{I}$
$=\frac{25 \times \frac{1}{5}}{0.4}$
$=12.5\, s ^{-2}$