Q.

A ball suspended by a thread swings in a vertical plane so that its magnitude of acceleration in the extreme position and lowest position are equal. The angle (θ) of thread deflection in the extreme position will be ______.                   [2024]

1 tan-1(2)  
2 2tan-1(12)  
3 tan-1(12)  
4 2tan-1(15)  

Ans.

(2)

Loss in kinetic energy = Gain in potential energy

12mv2=mg(1-cosθ)

v2=2g(1-cosθ)

Acceleration at lowest point =v2

Acceleration at extreme point =gsinθ

 v2=gsinθ

 sinθ=2(1-cosθ)

tanθ2=12θ=2tan-1(12)