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Problem 4 - Olympiad

A projectile's kinetic energy reduces by 25% due to air resistance. What fraction of its initial horizontal momentum is retained?

Correct: A

If KE reduces by 25%, final KE = 0.75 KE₀. Since KE ∝ v², v becomes √(0.75) = √3/2. Momentum p ∝ v, so retained momentum is √3/2.