A point mass m is moved in a vertical circle of the radius r with the help of a string. The velocity of the mass is 7 g r at the lowest point. The tension in the string at the lowest point is:

Step-by-step solution

First, make the free body diagram when a mass bob is attached with a string of length, r rotating in a vertical circle. Given, v = 7 g r , now make the equation between centripetal force and surface tension which are acted in opposite direction, ⇒ T - m g = m ( 7 g r ) 2 r ⇒ T = 8   m g .