Physics Help Forum Retrograde motion of Mars

 Feb 1st 2018, 09:38 PM #1 Junior Member   Join Date: Feb 2018 Posts: 2 Retrograde motion of Mars I have an annoying Physics question that I have been trying to work at for about 3 hours now, the class I'm taking is Calculus based but I'm not even sure if this question is necessarily calculus-related, I'm not sure how I should be approaching it. Here is a link because of the subscripts and notation not being transferrable... I've tried graphing these functions, but I'm pretty sure I'm not doing it correctly or I don't know how to analyze it, especially with an extra 't' factor. I also tried to relate all of it in terms of the Earth, and then in terms of Mars, but nothing seems to be resulting in progress. I have also tried subtracting both and doing the dot product but I don't know what to do from there, and it doesn't seem like they lead to anything. I have went to my TA's office hours and he doesn't understand it either.
 Feb 2nd 2018, 01:42 AM #2 Senior Member   Join Date: Oct 2017 Location: Glasgow Posts: 341 Maybe it will help to consider a much simpler example problem and then try and apply the same technique to the more difficult problem. Let's say we have two points on a graph, A and B. The vector that points from the origin to A is $\displaystyle \vec{OA} = 3i + 2j$ The vector that points from the origin to B is $\displaystyle \vec{OB} = -i + 6j$ How would you calculate the vector that points from A to B ($\displaystyle \vec{AB}$)? What is the magnitude and direction of the vector $\displaystyle \vec{AB}$?
Feb 4th 2018, 11:49 AM   #3
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 Originally Posted by Phantoful I have an annoying Physics question that I have been trying to work at for about 3 hours now, the class I'm taking is Calculus based but I'm not even sure if this question is necessarily calculus-related, I'm not sure how I should be approaching it. Here is a link because of the subscripts and notation not being transferrable... I've tried graphing these functions, but I'm pretty sure I'm not doing it correctly or I don't know how to analyze it, especially with an extra 't' factor. I also tried to relate all of it in terms of the Earth, and then in terms of Mars, but nothing seems to be resulting in progress. I have also tried subtracting both and doing the dot product but I don't know what to do from there, and it doesn't seem like they lead to anything. I have went to my TA's office hours and he doesn't understand it either.
Retrograde motion means that the motion of Mars relative to the distant stara appears to move. So determine the relative vector betwwen them as a starting point. I haven't tried it but that's where I'd start. We're not allowed to do the problem for you, just help.

 Tags calculus, mars, motion, retrograde, vectors

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