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First Law of Motion

A child stand...

Question

A child stands at the centre of a turntable with his two arms outstretched. The turntable is set rotating with an angular speed of 40 rpm. How much is the angular speed of the child if he folds his hands back and thereby reduces his moment if inertia to 2/5 times the initial value? Assume that the turntable rotates without friction.

A

16 rpm

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B

100 rpm

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C

40 rpm

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D

Given data is not sufficient

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Solution

The correct option is B
100 rpm

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Similar questions

Q. (a) A child stands at the centre of a turntable with his two arms outstretched. The turntable is set rotating with an angular speed of 40 rev/min. How much is the angular speed of the child if he folds his hands back and thereby reduces his moment of inertia to 2/5 times the initial value ? Assume that the turntable rotates without friction.
(b) Show that the childs new kinetic energy of rotation is more than the initial kinetic energy of rotation. How do you account for this increase in kinetic energy?

Q. A man, standing on a turn-table, is rotating at a certain angular frequency with his arms outstretched. He suddenly folds his arms. If his moment of inertia with folded arms is

75 %

of that with outstretched arms, his rotational kinetic energy will

Q. A man of mass

100 k g

stands at the rim of a turntable of radius

2 m

and moment of inertia

4000 k g m^{2}

mounted on a vertical frictionless shaft at its center. The whole system is initially at rest. The man now walks along the outer edge if the turntable(anticlockwise) with a velocity of

1 m / s

relative to earth. With what angular velocity and in what direction does the turntable rotate?

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