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
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