1) The distance between a point, X, in space and the centre of the Earth is 25 times the radius of Earth. If the gravitational field strength on the surface of the Earth is 9.81 N kg^–1, what is the gravitational field strength due to Earth at X?

2) The Earth experiences gravitational forces from the Sun, mass M_S, and from the Moon, mass M_M. The distance of the Sun from the Earth is r_S and the distance of the Moon from the Earth is r_M. What is the ratio of the force on the Earth due to the Sun to the force on the Earth due to the Moon?

3) A rock is thrown vertically upward near the surface of Planet X with a velocity of 45 m s^–1 and it comes to an instantaneous rest 5.2 s later. If the same rock is now thrown up near the surface of Planet Y with the same initial velocity as that on Planet X, at 5.2 s later it is still moving upwards at a speed of 25 m s^–1. If both planets do not have atmosphere, what is the ratio of the gravitational field strength near the surface of Planet Y to that of Planet X?

4) Which statement about a geostationary satellite is true?

5) An experimental satellite is found to have a weight W when assembled before launching from a rocket site. It is placed in a circular orbit at a height h = 6R above the surface of the Earth (of radius R). What is the gravitational force acting on the satellite whilst in orbit?