Question

In the previous question, if the particle is released from rest at its highest position then the tension in the rod 

(a) is zero when it is vertical 

(b) is zero when it is horizontal 

(c) is zero when it is making an angle of cos ^-1 (2/3) with the vertical 

(d) cannot be zero in any position

Answer 1

Correct Answer is: (c) is zero when it is making an angle of cos ^-1 (2/3) with the vertical

Applying the principle of conservation of energy between A and B,

mg (l - lcos θ) = 1/2 mv²

or mv² / l = 2mg (1 - cos θ) =  mgcos θ.

[The only force towards C is mgcos θ as T = 0.]

or cos θ = 2/3.