Question

A particle weighs 120N on the earth surface at what height above the ground will it's weight be 30N ?radius of earth 6400km

Answer 1

Surface on earth g = GM/R^2                   ---------------- (1)
At height h = Gm(R+h)^2                          ---------------- (2)


On solving both equations, we get

1/4 = R^2/(R+h)^2

4 = (R+h)^2/R^2

2 = (R+h)/R

R+h =2R

h = R

h = 6400.            (Given R=6400)


So, the height will be 6400 km.


Hope this helps!