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Question:

Body A of mass 4m moving with speed u collides with another body B of mass 2m, at rest. The collision is head on and elastic in nature. After the collision the fraction of energy lost by the colliding body A is :

89

19

49

59

Solution:

Correct option is B.
Fractional loss of KE of colliding body,
ΔKE/KE = 4×(m1m2)/(m1+m2)² = 4×(4m)×2m/(4m+2m)² = 32m²/36m² = 8/9