Q.

A circular platform is mounted on a vertical frictionless axle. Its radius is r=  2 m and its moment of inertia I=200 kg m2. 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 v0=1 ms-1 relative to the ground. The angular velocity of the platform is

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a

0.4 rads-1

b

0.7 rads-1

c

1.2 rads-1

d

2 rads-1

answer is C.

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Detailed Solution

As the system is initially at rest, therefore, initial angular momentum, Li=0.

According to the law of conservation of angular momentum, final angular momentum, Lf=0

  Angular momentum of man = angular momentum of platform in opposite direction

i.e., mv0r=Iω

or  ω=mv0rI=70(1.0)(2)200=0.7rads-1

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A circular platform is mounted on a vertical frictionless axle. Its radius is r=  2 m and its moment of inertia I=200 kg m2. 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 v0=1 ms-1 relative to the ground. The angular velocity of the platform is