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A rubber ball is dropped from a height of 5 m onto a floor. After each bounce it rises to 81/100 of the height from which it fell. Find the average speed of the ball over its entire motion. (Take g = 10 m s⁻²)

1. 3.0 m s⁻¹
2. 3.50 m s⁻¹
3. 2.0 m s⁻¹
4. 2.50 m s⁻¹

Correct answer: 3.50 m s⁻¹

Solution

Total distance and total time are summed as geometric series; with h = 5 m, r = 0.81, the average speed works out to 3.5 m/s.

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