A mass attached to string of length 0.4 m is rotated in vertical circle with minimum possible speed

Question

A mass attached to string of length 0.4 m is rotated in vertical circle with minimum possible speed (critical speed). The speed at bottom most point is ( $g=10 \mathrm{~m} / \mathrm{s}^2$ )

Professor PC Thomas Classes · Answer

The minimum speed at the lowest point to complete a vertical circle is $\sqrt{5gR}$. Here, $R = 0.4 \mathrm{m}$. So, $v = \sqrt{5 	imes 10 	imes 0.4} = \sqrt{20} \mathrm{m/s}$.