1. When a body of mass 'm' is taken from the surface of the earth to a height equal to the radius of the earth (R) then the change in its Potential energy is______ got the solution as follows: 1) when on the surface of the earth the P.E is mgR (considered it as initial P.E) when the body is taken to height 'h=R' frm the surface of earth the P.E is mg(R+R) = 2mgR (considered it as final P.E) .. . change = Final P.E - Initial P.E = 2mgR-mgR= mgR another approach: 2) on the surface of earth P.E = 0 when raised to "h=R" its P.E = mgR . . . change in P.E= mgR out of these two approaches which is considered to be the best.