# Homework Help: Charge moving in elliptical orbit under Coulomb field.

1. Jul 8, 2012

### AGNuke

Under the influence of the coulomb field of charge +Q, a charge −q is moving around it in an elliptical
orbit. Find out the correct statement(s).
(A) The angular momentum of the charge −q is constant
(B) The linear momentum of the charge −q is constant
(C) The angular velocity of the charge −q is constant
(D) The linear speed of the charge −q is constant

I am blank at this one. I don't know how to find either one, especially since this is elliptical orbit.

All I know is that since it is elliptical orbit, speed is not constant, so is velocity and thus, linear momentum. Now I am confused between what is constant, angular velocity or angular momentum.

I tried balancing electrostatic force with centrifugal force at any arbitrary point, but so far, I didn't got any satisfactory conclusions from my efforts.

2. Jul 8, 2012

### grzz

If there is no torque on the charge then its angular momentum is constant.

3. Jul 8, 2012

Oh! Thanks.