A person standing near the edge of the top of a building throws two balls A and B. The ball A is thrown vertically upward and B is thrown vertically downward with the same speed. The ball A hits the ground with a speed and the ball B hits the ground with a speed We have
The initial energy of the ball A and ball B ( at the top of the building, at the time of throwing is equal since both are at equal height () and thrown with same speed (). That is
The final energy of ball A at ground will be
The final energy of ball B at ground will be
By conservation of energy, Initial energy=Final energy
Since initial energies of ball A and ball B are equal (equation (1)), using equation (2), (3) and (4), their final energies are also equal