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Question:

A circular platform is mounted on a frictionless vertical axle. Its radius R = 2m and its moment of inertia about the axle is 200 kgm². It is initially at rest. A 50 kg man stands on the edge of the platform and begins to walk along the edge at the speed of 1 m/s relative to the ground. Time taken by the man to complete one revolution is?

πs

3π/2s

π/2s

2πs

Solution:

By applying the law of conservation of angular momentum, I₁ω₁ + I₂ω₂ = 0
200(0) + 200ω₂ = 0
ω₂ = 0
ωR = ω₁ - ω₂ = 1 rad/sec
T = 2π/ω = 2π sec