Question

A sphere is suspended by a thread of length $l$ . The minimum horizontal velocity which has to be imparted to the sphere for it to reach the height of suspension is

• A. $2\sqrt{g l}$
• B. $\sqrt{2 g l}$
• C. $\sqrt{g l}$
• D. $4\sqrt{g l}$

Answer 1

Answer: (B)

Kinetic energy at $A=\frac{1}{2}mu^{2}$
Potential energy at $B=mgh$
For conservation of energy, $\frac{1}{2}mu^{2}=mgl$
$u=\sqrt{2 g l}$