Q5.26 A stone of mass m tied to the end of a string revolves in a vertical circle of radius R. The net forces at the lowest and highest points of the circle directed vertically downwards are : [Choose the correct alternative]
Lowest Point Highest Point
(a)
(b)
(c)
(d)
and denote the tension and speed at the lowest point,
and denote corresponding values at the highest point.
The FBD of the stone at the lowest point is shown below :
According to Newton’s second law of motion, the net force acting on the stone at this point is equal to the centripetal force, i.e.,
Where, v = Velocity at the lowest point
The FBD of the stone at the highest point is given below :
Using Newton's law of motion we have :
Where v = Velocity at the highest point
It is clear from the above equations that the net force acting at the lowest and the highest points are respectively (T – mg) and (T + mg).