- #1
GwtBc
- 74
- 6
Member advised to use the formatting template for questions posted to the homework forums
Hi all.
Our lecturer gave us an exercise the other day regarding an elastic gravitational collision between a planet and a satellite where the satellite slingshots using the gravitational field of the planet. The question asks to show that ##v_{f} - v_{i} = 2v_{0}## where ##v_{f}## is the final velocity of the satellite, ##v_{i}## is it's initial velocity and v_{0} is the orbital speed of the planet. The hint is to translate this problem into the COM reference frame, which I did do, and got:
##p'_{i} = m(v_{i}- v_{0})##
and
##p'_{f} = m(v_f + v_0)##
. I was told by someone that I can't do this since the planet isn't an inertial frame, I thought it would be ok since the acceleration of M is extremely small,. But I'm still not sure since if the equations for the momentum of the system from the lab's reference frame are written out and then translated into the planet's reference then there's an ##M\delta v## term in the second equation which is absurd since the planet can't be moving in it's own ref frame. Also this implies that ##v_{f} + v_{0}## and ##v_{i} - v_{0}## are equal whilst they're in opposite directions. I hope someone can set me on the right track .
Our lecturer gave us an exercise the other day regarding an elastic gravitational collision between a planet and a satellite where the satellite slingshots using the gravitational field of the planet. The question asks to show that ##v_{f} - v_{i} = 2v_{0}## where ##v_{f}## is the final velocity of the satellite, ##v_{i}## is it's initial velocity and v_{0} is the orbital speed of the planet. The hint is to translate this problem into the COM reference frame, which I did do, and got:
##p'_{i} = m(v_{i}- v_{0})##
and
##p'_{f} = m(v_f + v_0)##
. I was told by someone that I can't do this since the planet isn't an inertial frame, I thought it would be ok since the acceleration of M is extremely small,. But I'm still not sure since if the equations for the momentum of the system from the lab's reference frame are written out and then translated into the planet's reference then there's an ##M\delta v## term in the second equation which is absurd since the planet can't be moving in it's own ref frame. Also this implies that ##v_{f} + v_{0}## and ##v_{i} - v_{0}## are equal whilst they're in opposite directions. I hope someone can set me on the right track .