A ball hits a smooth horizontal floor moving at 45 deg to the vertical. Taking the coefficient of restitution e <= 1, which of the following CANNOT be the angle that its velocity makes with the vertical just after the bounce?

45 deg
30 deg
53 deg
60 deg

Correct answer: 30 deg

Solution

Since the vertical component is reduced (or unchanged) while horizontal stays the same, the rebound angle from the vertical must be >= 45 deg; 30 deg is impossible.

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