Question

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 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 1

Answer: (C)

0.7 rad s-1

Answer 2

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

According to the law of conservation of angular momentum final angular momentum,

$\therefore$ angular momentum ofj man = angular momentum of platform in opposite direction

i.e.,

or,