Question

A particle weighs 120 n on the surface of the earth.at what height above the earth's surface will its weigh be 30 n?

Answer 1

mass of the partilce remains same i.e. monly the aceleration due to gravitation varies because of increase in distancelet the height be hthus on surface of earth, F = 120N = GMm/R2 (R is the radius of earth)then at height h, F' = 30N  = GMm/(R+h)2dividing these two equations we get4 = (R+h)2 / R2or 2  = (R+h)/Ror h = Rthus at a height of 6400 km ( radius of earth = 6400 km)