A child throws a ball vertically upwards at 8 m/s. It takes 3.3 seconds to reach its maximum height. Let us assume the frictional force of air can be ignored. Let the point from where the ball was thrown upwards have height 0. When the ball is thrown, it has a potential energy 0 and its kinetic energy is (1/2)*m*8^2 , where m is the mass of the ball. As the ball rises, its velocity decreases which leads to the kinetic energy falling and the potential energy of the ball increasing. If the maximum height that the ball reaches is H, at this point the velocity and kinetic energy of the ball is 0 and its potential energy is m*g*H where g is the gravitational acceleration.

The ball then starts to fall and comes back to the point where it was thrown up from. The potential energy of the ball is now 0 and the velocity of the ball is again 8 m/s in the downward direction.

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