If the Earth were to suddenly contact to half its present radius, by how much would the day time decrease ?

Explanation

From the law of conservation of angular momentum,
`I_1omega_J=I_2omega_2` where `omega_1=(2pi)/(T)`
hence `(I_1)/(T_1)=(I_2)/(T_2)` where I=`2/5MR^2` if M remains the same, then
`T_2=((R_1)/(R_1))^2.T_1((1R)/(2R))^2(24)=6`hr.
`:. /_\T=24-6=18`hr. Decrease in the period of rotation is 18 hr.