A body weighs 64 N on the surface of the earth. What is the gravitational force (in N) on it due to the earth at a height equal to one-third of the radius of the earth ?

Here, mg=64N; h=R/3The value of acceleration due to gravity at a height h (when h is not negligible as compared to R),g′=gR2(R+h)2Or  mg′=mgR2(R+h)2=64×R2(R+R/3)2=64×916=36 N