Question

19. A body of mass 'm' attached to a string is rotating
in a vertical plane with velocity 'V'. The tension of the
string is maximum when the string is
(A) vertical and the body is at the lowest position.
(B) vertical and the body is at the highest position.
(C) horizontal and the body is moving downwards.
(D) horizontal and the body is moving upwards.​

Answer 1

answer : option (A) vertical and the body is at the lowest position.

explanation : A body of mass 'm' attached to a string is rotating

in a vertical plane with velocity ‘v’. Let l is the length of string.

now tension in string

case 1 : at lowest position,

upward force - downward force = mv²/l

or, T - mg = mv²/l

or, T = mg + mv²/l

case 2 : at highest position,

downward force - upward force = mv²/l

(T + mg) - 0 = mv²/l

or, T = mv²/l - mg

case 3 : horizontal line ,

net force along horizontal line = mv²/l

or, T = mv²/l

from above explanation it is clear that tension in string will be maximum when body is at lowest position