# Gravitation and potential energy

1. Jun 19, 2010

### cuman12

In the example 12.5 (Section 12.3) in the textbook we ignored the gravitational effects of the moon on a spacecraft en route from the earth to the moon. In fact, we must include the gravitational potential energy due to the moon as well. For this problem, you can ignore the motion of the earth and moon.

A) If the moon of mass m(m) has radius R(M) and the distance between the centers of the earth and the moon is R(EM), find the total gravitational potential energy of the particle-earth and particle-moon systems when a particle with mass m is between the earth and the moon, and a distance r from the center of the earth. Take the gravitational potential energy to be zero when the objects are far from each other. Take the mass of earth as m(E)

B) There is a point along a line between the earth and the moon where the net gravitational force is zero. Use the expression derived in part (a) to find the distance of this point from the center of the earth.

C) With what speed must a spacecraft be launched from the surface of the earth just barely to reach this point?

D) If a spacecraft were launched from the earth's surface toward the moon with an initial speed of 11.2 {\rm km/s}, with what speed would it impact the moon?

2. Jun 19, 2010

### Fightfish

Perhaps it would help if you would show where you encountered problems in your attempts to solve this problem?

3. Jun 19, 2010

### cuman12

It was in mastering physics

4. Jun 19, 2010

Try!