Question

A circular disc is rotating in horizontal plane about its own axis at the rate of $210rpm$. A coin of mass $10gm$ is placed on the disc at a distance $10cm$ from the axis. If the coin does not skid, the frictional force between the coin and the disc is:

• A. $0.242N$
• B. $0.484N$
• C. $0.844N$
• D. $1.26N$

Answer 1

The correct option is B $0.484N$

Friction$\left(f\right)$ is balancing the centripetal force

$f=m{\omega }^{2}r$
$=10\times {10}^{-3}\times 0.1\times (\frac{210\times 2\pi }{60}{)}^2$
$=0.484N$