If earth shrink (without change in mass) to half it's present size. Length of the day would become `6` hours.
As size of earth changes its moment of inertia changes.

Options

A. If both assertion and reason are true and the reason is the correct explanation of the assertion.
B. If both assertion and reason are true but reason is not the correct explanation of the assertion.
C. If assertion is true but reason is false.
D. If the assertion and reason both are false.

Answer

A

Explanation

When earth shrinks it angular momentum remains constant .i.e. `L=Iomega=(2)/(5)mR^(2)xx(2pi)/(T)`=constant .
`:.T prop I prop R^(2)`. It means if size of the earth changes then its moment of inertia changes.
In the problem radius becomes half so time period (Length of the day) will becomes 1/4 of the present value i.e.24/4=6 hr.