Question

A circular disc of mass 20kg and radius 15cm is mounted in an horizontal cylindrical axle of radius
1.5cm. Calculate the K.E of the disc after 1.2sec if s force 12N is applied tangentially to the axle.

Answer 1

$KE=I\omega^2/2$

$I=mR^2/2=20\cdot0.15^2/2=0.225\ (kg\cdot m^2)$

$\omega=\epsilon t$

$M=I\epsilon \to \epsilon=M/I=12\cdot0.015/0.225=0.8\ (rad/s^2)$

$\omega=0.8\cdot 1.2=0.96\ (rad/s)$

$KE=I\omega^2/2=0.225\cdot0.96^2/2=0.104\ (J)$ . Answer