Sphere B of 20 kg is at rest on a shelf and receives the impact of another equal sphere. The distance from the ceiling to the center of the sphere is 2 m and the restitution coefficient is 0.7. At the moment of impact the thread is vertical and the center of sphere A is at the same level as the lowest point of sphere B.

Determine the angle θ from which the sphere A will be released so that the sphere B travels a distance of 1.5 m before touching the horizontal surface again.

 

Fig.04