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  4. Assertion If the ice on the polar caps of the earth melts, then length of day will increase. Reason Moment of inertia of the earth increases, as ice on polar caps melts.

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Q. Assertion If the ice on the polar caps of the earth melts, then length of day will increase.
Reason Moment of inertia of the earth increases, as ice on polar caps melts.

AIIMSAIIMS 2014

Solution:

When the ice on the polar caps melts, the mass concentrated near the axis of rotation is spread out. The moment of inertia of system increases. Since, no external torque acts on the system. $l \omega=$ constant .
Therefore, if $l$ increases, the angular speed will decrease. So, the time period of rotation of the earth $\left(T=\frac{2 \pi}{\omega}\right)$ increases i.e., the duration of the day will increase.