Question

A cord of negligible mass is wound round the rim of fly wheel of mass 20 kg and radius 20 cm. A steady pull of 25 N is applied on the cord as shown in the figure. The fly wheel is mounted on a horizontal axle with frictionless bearings. Compute the angular acceleration of the wheel.

• A. $8.25kg{m}^2$
• B. $6.25kg{m}^2$
• C. $4.8kg{m}^2$
• D. $1.0kg{m}^2$

Answer 1

The correct option is B $6.25kg{m}^2$

Given : $M=20$ kg $R=0.2$ m $F=25$ N

Using $\tau =I\alpha$

$\therefore$ $FR=\left(M{R}^2\right)\alpha$ $⟹\alpha =\frac{F}{MR}$

Thus, angular acceleration $\alpha =\frac{25}{20\times 0.2}=6.25$ $rad/s^2$