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The angular momentum vector for a spinni...

The angular momentum vector for a spinning wheel lies along its axle and is pointed north. To make this vector point east with chagin magnitude it is necessary to exert a force of constant magnitude on the north end of the axle in which direction?

A

always up

B

always down

C

at the initial moment in the east direction, but the force always remain perpendicular to the axle

D

always in the east direction

Text Solution

Verified by Experts

The correct Answer is:
A

Let the wheel rotate by a small angle `d theta`. Then `vec(dL)` is along east, because magnitude of `vecL` remains the same. But the torque is in the direction of change in angular momentum. So the torque should be along east. For this, the force should be in the upward direction.
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