Q:A body is thrown up in a lift with a velocity ‘u’ relative to the lift and the time of flight is t. Show that the lift is moving up with an acceleration (2u-tg)/t.

Using the concept the relative motion and eqn. v=u+at, I’ve managed till a= (u+v-tg)/t but i am not able to conclude how final velocity (i.e., v) before striking the ground equals the initial velocity (u) with which the ball was thrown, since the lift is accelerating upwards (which means that the ball will hit the ground of the lift before aquiring its initial velocity).

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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