Question

A disc is rotated about its axis with a certain angular velocity and lowered gently on a rough inclined plane as shown in figure, then

• A. It will rotate at the position where it is placed and then will move downwards
• B. It will go downwards just after it is lowered
• C. It will go downwards first and then climb up
• D. It will climb upwards and then move downwards

Answer 1

The correct option is A It will rotate at the position where it is placed and then will move downwards

Initially, the disc was sliding thus kinetic friction will act.

$f=\mu mgcos30=\frac{1}{\sqrt{3}}mg\times \frac{\sqrt{3}}{2}=\frac{mg}{2}$

As the force $mgsin30$ balances the $f$, thus the disc will rotate at its position initially. But the friction force tends to reduce the angular velocity.

When it reverses the direction of angular velocity, then the disc will move downwards rolling purely.