1. In the picture two spheres of mass m and a third sphere of mass M form an equilateral triangle and a fourth sphere of mass m 4 is at the center of the triangle. The net gravitational force on that central sphere from the three other spheres is zero.

(a) What is M in terms of m ?

(b) if we double the value of m 4 , what then is the magnitude of the net gravitational force on the central sphere ?

2. The fastest possible rate of rotation of a planet is that for which the gravitational force on material at the equator just barely provides the centripetal force needed for the rotation. (why ? ) (A) show that the corresponding shortest period of rotation is

3. Two concentric shells of uniform density having masses M 1 and M2 are situated as shown in the picture. Find the magnitude of the net gravitational force on a particle of mass m , due to the shells, when the particle is located at (a) point A at distance r = a from the center (b) point B at r = b and (c) point C at r = c. The distance r is measured from the center of the shells.

4. A satellite hovers over a certain spot on the equator of (rotating ) earth. What is the altitude of its orbit (called a geosynchronous orbit )

5. A 150.00 kg rocket moving radially outward from Earth has a speed of 3.70 km/s when its engine shuts off 200 km above earths surface.

(a) assuming negligible air drag, find the rockets kinetic energy when the rocket is 1000 km above Earths surface.

(b) what maximum height above the surface is reached by the rocket ?