Question
Fri September 13, 2013 By: Rajneesh Kumar

A particle weight 120N on the surface of the earth. At what height above the earth's surface will its weight be 30N? Radius of the earth= 6400 Km.

Expert Reply
Fri September 13, 2013
mass of the partilce remains same i.e. m
only the aceleration due to gravitation varies because of increase in distance
let the height be h
thus on surface of earth, F = 120N = GMm/R2 (R is the radius of earth)
then at height h, F' = 30N  = GMm/(R+h)2
dividing these two equations we get
4 = (R+h)2 / R2
or 2  = (R+h)/R
or h = R
thus at a height of 6400 km
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