Q. A block of mass $m$ at the end of a string is whirled round in a vertical circle of radius $R$. The critical speed of the block at the top of its swing below which the string would slacken before the block reaches the top is
A) $Rg$
B) $(Rg)^{2}$
C) $R/g$
D) $\sqrt{Rg}$
Explanation
(d) At highest point $\frac{mv^{2}}{R} = mg\ \Rightarrow v = \sqrt{gR}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.