A solid sphere and a hollow sphere of identical mass and radius roll down the same incline from rest. Which reaches the bottom first?

Answer and explanation

Correct answer: D. The solid sphere

  1. Step 1: Solid sphere I = (2/5)MR^2; hollow sphere I = (2/3)MR^2. Step 2. Acceleration a = gsin(theta) / (1 + I/(MR^2)). For solid a = 5/7gsin(theta); for hollow a = 3/5gsin(theta). Answer: The solid sphere. Why not the others: The solid sphere has higher linear acceleration and reaches the bottom first.

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