Question

Question 5.26 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) mg – T1 mg + T2



(b) mg + T1 mg – T2



(c) mg + T1 –/R mg – T2 + /R



(d) mg – T1 – /R mg + T2 + /R




T1 and v1 denote the tension and speed at the lowest point. T2 and v2 denote corresponding values at the highest point.

Chapter Laws Of Motion Page 112

Answer 1

Let T1 and T2 are tension in string at lowest and highest position in the vertical cirlcle respectively.


AT lowest position ,
Tension in string always towards the centre of the circle.hence, T1 acts toward the centre.
At lowest position string stretched downward due to weight of stone (mg) act downard direction. So,net Force act downwards direction .
So, net Force = downard force - upward force = mg - T1

At highest position ,
T2 acts twoard the centre( e.g downwards ) and mg act downward.
Hence, net Force acting on the stone in downward direction = downward force - upward force
= mg + T2 - 0
= mg + T2
Hence, option (A) is correct