question_answer

If an iron ball and a wooden ball of the same radius are released from a height h in vacuum, then time taken by both of them to reach the ground will be

A)  zero                                     

B)  unequal

C)  roughly equal  

D)  exactly equal

Correct Answer: D

Solution :

                 The centripetal force required to keep the ball in circular motion is                 \[F=\frac{m{{v}^{2}}}{r}\] where m is mass, v the velocity and r the radius                 \[\therefore \]  \[v=\sqrt{\frac{Fr}{m}}\]              \[(\because r=l)\]            Given,   \[F=25\,N,\]   r = 1.96 m,               m = 0.25 kg \[\therefore \]  \[v=\sqrt{\frac{25\times 1.96}{0.25}}=\sqrt{196}\] \[\Rightarrow \]               v = 14 m/s