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Thermal Expansion

An ice block ...

Question

An ice block is in a trough which is rotating about vertical axis passing through its centre. When ice melts completely, the angular velocity of the system

A

Increases

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B

Decreases

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C

Remains same

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D

Becomes double

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Solution

The correct option is B
Decreases

When the ice melts completely, the distribution of mass is more at the farther points from the axis of rotation which increases moment of inertia.
$∴$ Applying conservation of angular momentum,
$I_{1} ω_{1} = I_{2} ω_{2}$
$ω_{2} = \frac{I_{1} ω_{1}}{I_{2}}$
As $I_{2} > I_{1}, ω_{2} < ω_{1}$
$∴$ Angular velocity of the system decreases.

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