A person stands on a spring balance at the equator. (a) By what fraction is the balance reading less than his true weight? (b) If the speed of earth’s rotation is increased by such an amount that the balance reading is half the true weight, what will be the length of the day in this case?
As he is standing on a rotating extraterrestrial body, he will feel centrifugal force which will try to eject him form the body. Force of gravity will pull the guy towards the center.
As the guy is not moving anywhere, he is in an equilibrium with the reaction force.
The actual weight of the body,
So, the decrement will be,
Angular speed of earth is,
So, it will decrease at a rate,
= 3.5 × 10-3
(b) 2.0 hour
According to the condition 
1