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Tuesday, August 14, 2012

Q.418. Gravitation.

Question 418.
The radius of the earth is R and its angular velocity is W (omega) . If the earth suddenly stops rotation, then the change in the value of g at a place on the equator will be :
A- zero          B-RW          C- R/W^2          D- RW^2.

Answer 418.
g is the acceleration experienced by the body on the surface of the earth.
The body of mass m on the surface of the earth exerts a force on the surface equal to its weight, mg and has a reaction from the surface of the earth = N
The net force on the body of mass m = mg - N provides the centripetal force needed for the revolution of the object on the surface on the circle of radius R with angular velocity W
=> mg - N = mRW^2
=> N = mg - mRW^2
N is the weight recorded on the balance = mg'
=> mg' = mg - mRW^2
=> m(g - g') = RW^2
=> g - g' = RW^2 which is the difference in acceleration due to gravity when the earth is rotating and when it stops rotating.

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