Solving Rotational Problem: Satellite Elliptical Orbit, Torque & Speed

[Anthonyphy2013]

Homework Statement

A satellite follows an elliptical orbit. The only force on the satellite is the gravity atraction from the planet. The satellites speed at point A is 8000m/s, and it is 6000km away, Point B is 24000km east of the planet, and Point C is component vector 9000ikm+12000jkm away, if the you take the planet as the origin.

a. Is there any torque acting on the satellite?
b. satellite speed at Point B
c, satellite speed at Point C

Homework Equations

torque = force*R

The Attempt at a Solution

part a, I consider there is no torque since the only force is parallel to the pivot . Does it make sense.
part b ,since my professor does not mention gravitational force on this question , I use the f=mv^2/r to this question. i know there is no torque , and I know the radius is changing and I assume the gravitational force for at point a , b and c are the same and then I apply f=mva^2/ra = mvb^2/r2 . is that a good way to solve this problem ?

 

[pgardn]

Have you guys covered conservation of angular momentum?

 

[Anthonyphy2013]

yes , but how could angular momentum , L=mvr could apply to this question ?

 

[pgardn]

Well the mass of the satellite does not change. And it has the same angular momentum at every place in its orbit with respect to the planet...

 

[pgardn]

V*r = V'*r'

Familiar?