Question

A pendulum bob of mass $10g$ is attached to a rod of length $2m$ and is allowed to move in the vertical circle. Find the minimum velocity of bob at the bottom of the circle so that the bob completes the circle.
(Take $g=10m/s^2$)

• A. $10m/s$
• B. $8.9m/s$
• C. $0.89m/s$
• D. $9m/s$

Answer 1

The correct option is B $8.9m/s$

Applying energy conservation at the lowest point

$\frac{1}{2}m{v}^2=mg\left(2R\right)$

$v=\sqrt{4gR}$, this is the critical velocity of the bob at the bottom most position for looping the loop

$v=\sqrt{4\times 10\times 2}$

$v=\sqrt{80}=8.9m/s$

Hence option B is the correct