Question

Q. If earth suddenly stop rotating. then the weight of an object of mass m at equator will [ω is angular speed of earth and R is its radius]

Decrease by mω2R

Increase by mω2R

Decrease by mω R2

Increase by mω R2

Answer 1

In rotating condition mass at equator is mg-mRω2

if earth stops rotation then it will become mg so INCREASES BY mRω2

This is bcoz........
Acceleration due to gravity will increase.

As the Earth is rotating about itself, all objects and people are going around in a circle every day.  In order to move in a circle like that there is a force required.  Thus some part of the gravitational force makes us go around in that circle.  The remaining force is equal to the apparent or observed weight of an object on the surface of earth.   So apparent weight is less than true weight.

If Earth is not rotating about itself,  then all the gravitational force of attraction is equal to the weight.  Hence the apparent weight is same as true weight.
SO NONE OF YOUR OPTIONS ARE CORRECT
but the correct answer is
INCREASES BY mRω2