Just need some clarification

  • Thread starter highc
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  • #1
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I'm working through a problem that was posted here a while ago (https://www.physicsforums.com/showthread.php?t=115170). maltesers posted the equation (Gm)/(r-S)^2 = (GM)/r^2, so far this makes perfect sense, he then goes on to solve for S with S = r - (mr^2)/M, and it is here that he loses me. How did we eliminate the ^2 to go from (r-S)^2 to S = r - ...?

I've been out of the math game a little too long!
 

Answers and Replies

  • #2
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That equation is actually incorrect. It should have been

[tex]\frac{Gm}{(r-S)^2} = \frac{GM}{S^2}[/tex]
 
  • #3
George Jones
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neutrino said:
That equation is actually incorrect. It should have been

[tex]\frac{Gm}{(r-S)^2} = \frac{GM}{S^2}[/tex]
This not the only thing wrong.

Look at units. In maltesers' last equation, S is a length, while the last term on the right has units of length squared.
 
  • #4
2,063
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George Jones said:
This not the only thing wrong.

Look at units. In maltesers' last equation, S is a length, while the last term on the right has units of length squared.
Now that it's known that the original equation is wrong, why bother about what was derived from it. :tongue2:

Thanks for pointing that out.
 
  • #5
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Thanks alot, I wasted way too much time on this one.
 

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