Question

In a simple pendulum the breaking strength of the string is double the weight of through bob.the bob is released from rest when the string is horizontal the string breaks when it makes an angle thita with the vertical

Answer 1

Tension = T. Angle with vertical = θ.
Speed of pendulum = v at θ.
Length of string = L

T = mg cosθ + m v^2/ L
m v^2 /2 = KE = m g L cosθ (loss in PE).

Solving these, T = 3 m g cosθ.
When the string snaps, T = 2 m g.

So cosθ = 2/3 . Answer.