- #1

Specter

- 120

- 8

## Homework Statement

The Earth has a mass of 5.98 x 10

^{24}kg and the moon has a mass of 7.35 x 10

^{22}kg. The distance from the centre of the moon to the centre of the Earth is 3.84 x 10

^{8}m. A rocket with a total mass of 1200 kg is 3.0 x 10

^{8}m from the centre of the Earth and directly in between the Earth and the moon. Find the net gravitational force on the rocket from the Earth and the moon.

## Homework Equations

Fnet = Gm1m2/r

^{2}

## The Attempt at a Solution

m1 (earth)=5.98 x 10

^{24}kg

m2 (moon)=7.35 x 10

^{22}kg

m3 (rocket)=1200kg

m1 is 3.85 x 10

^{8}m from the centre of m2

m3 is 3.0 x 10

^{8}m from the centre of m1

My problem is trying to figure out how far the rocket(m3) is from the moon(m2). The question says that the rocket is directly in between the Earth and the moon, so does that mean that the distance is 3.0 x 10

^{8}m to the centre of the moon and to the centre of the earth?

Next I would use Fnet = Gm

_{1}m

_{3}/r

_{13}+ Gm

_{2}m

_{3}/r

_{23}and solve the question. In the example I read it said "add their magnitudes since both forces act in the same direction". In this question the forces would be acting in different directions, one toward the moon and the other toward earth. Does this mean I subtract the magnitudes instead of adding?