A student at the top of a building of height h throws one ball upward with a spe

Question

A student at the top of a building of height h throws one ball upward with a speed of v_0 and then throws a second ball downward with the same initial speed v_0. How do the velocities of the balls compare just before they reach the ground, neglecting air resistance? The velocities are the same. The ball that started out upward has twice as great a velocity as the other ball. The ball that started out downward has twice as great a velocity as the other ball. The ball that started out upward has four times as great a velocity as the other ball. The ball that started out downward has four times as great a velocity as the other ball.

Explanation / Answer

Since the initial velocity Vo is same for both the balls the only force acting after the release of balls is gravity that is also same for both the balls, time taken by ball thrown upward is definitely more than the ball released downwards, but their velocities remains the same.

As per the conservation of energy and momentum, both the balls had same kinetic energy in the beginning so till they reach the ground they would have same kinetic energies,so the velocities must be same.

so option (a) is correct.

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