# Homework Help: Universal gravitational, elliptical orbits

1. Nov 18, 2009

### carbon_mc

1. The problem statement, all variables and given/known data
a spacecraft of mass 1000kg, in an elliptical orbit about the earth, at one point its distance from earth is 1.2 x 107 meters and its velocity is 7.1 x 103 meters per sec, and the velocity vector is perpendicular to the line connecting the center of the earth to the spacecraft. Mass of earth is 6.0 x 1024 kg and radius of earth is 6.4 x 106
Find the magnitude of the angular moemntum of the spacecraft about the center of the earth

2. Relevant equations

L = I $$\omega$$
L = r x p
$$\omega$$ = v/r
3. The attempt at a solution

ok so I know that energy and angular momentum is conserved. I know how to solve this but I just want to make sure. Do I just do this by finding the angular velocity by $$\omega$$ = v/r then multiplied by I which equals to mr2 . it sounds really weird so I just want to make sure.

2. Nov 18, 2009

### Dick

Just use L=rxp. What's the length of r, the length of p and the angle between them?

3. Nov 18, 2009

### carbon_mc

I think it's mvr .. they didnt say anything about angle or anything. the velocity vector is perpendicular so it's sin 90 = 1 .

4. Nov 18, 2009

### lanedance

so you shoul have all the info for L = r x p, which becomes |L| = r(mv).sin(theta) = r(mv) = mvr, when the velocity & position vector are perpindicular