Question

State law of conservation of momentum of angular momentum.
If the earth were to suddenly contract to half of its present radius (without any external torque on it) by what
duration would the day be decreased?( Assume earth to be a perfect solid sphere).​

Answer 1

1)Law of Conservation of Angular Momentum

Any of the individual angular momenta can change as long as their sum remains constant. This law is analogous to linear momentum being conserved when the external force on a system is zero.

2)So, for an Earth that is contracted to half its present size with mass constant, the duration of a day will be just 6hrs.