1.

A circular platform is mounted on a vertical frictionless axle. Its radius is `r = 2 m` and its moment of inertia`I = 200 kg m^2`. It is initially at rest. A `70 kg` man stands on the edge of the platform and begins to walk along the edge at speed `v_0 = 1 m s^-1` relative to the ground. The angular velocity of the platform is.A. `1.2 rad s^-1`B. `0.4 rad s^-1`C. `0.7 rad s^-1`D. `2 rad s^-1`

Answer» Correct Answer - C
( c) As the system in initially at rest, therefore, initial angular momentum, `L_i = 0`.
According to the law of conservation of angular momentum, final angular momentum, `L_f = 0`
:. Angular momentum of man = angular momentum of platform in opposite direction
i.e., `mv_0 r = I omega`
or `omega = (m v_0 r)/(I) = (70(1.0)(2))/(200) = 0.7 rad s^-1`.


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