A rubber ball is dropped from 5 m on a horizontal plane and rebounds to 1.8 m. By what fraction of its pre-impact speed is speed lost in the bounce?
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A rubber ball is dropped from 5 m on a horizontal plane and rebounds to 1.8 m. By what fraction of its pre-impact speed is speed lost in the bounce?

G1 Physics · Accepted Answer

Step 1 — Principle: The ratio of relative speed of separation to relative speed of approach is the coefficient of restitution. Step 2 — Working: Speed before impact is √(2g×5), speed after impact is √(2g×1.8). Step 3 — Working: Ratio after/before=√(1.8/5)=0.6=3/5; therefore fractional loss in speed is 1-3/5=2/5. Correct answer: B — 2/5.