How to find the angle{theta} when the question is given like this

que: two equal discs initially at rest are in contact on a table. a third disc of same mass but of double radius strikes them symmetrically and itself comes to rest after impact.the coeficient of restitution is

1] 2/3

2] 9/16

3] 3/4

4] 8/17

Three identical balls are placed on a frictionless horizontal surface touching each other. They stick to each other because of adhesive. Another ball of same radius and mass m is placed over the void created by the three balls. Find the forces applied by the balls kept on the floor to each other if the system remains in equilibrium.

A car loaded with water having total mass 1000 kg moves on a straight horizontal Road starting from rest under the action of a force of 100 Newton. The water spills throw a small hole in the bottom at a rate of 0.1 KG per second the velocity of cart after 300 seconds is nearly.

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