question_answer

A sphere is suspended by a thread of length \[l\]. What minimum horizontal velocity has to be imparted the ball for it to reach the height of the suspension  [ISM Dhanbad 1994]

A)             \[gl\]

B)                      \[2gl\]

C)             \[\sqrt{gl}\]     

D)             \[\sqrt{2gl}\]

Correct Answer: D

Solution :

                Kinetic energy given to a sphere at lowest point = potential energy at the height of suspension                         Þ \[\frac{1}{2}m{{v}^{2}}=mgl\]             \\[v=\sqrt{2gl}\]