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Easy physics question but dont get it

  1. Sep 11, 2009 #1
    A car travels along a certain road at an average speed of 42 km/h, and returns along the same road at an average speed of 52 km/h. Calculate the average speed for the round trip, to within 0.1 km/h.

    i have no clue. I'm trying to help a friend with general Physics homework (i've taken physics with calc) but i cant get this very simple question. please help!
  2. jcsd
  3. Sep 11, 2009 #2


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    This thread should be in the homework sub-forum.

    Anyway, how long does it take for the car to travel to a destination a distance [itex]x[/itex] away?
    How long does it take to get back?
  4. Sep 11, 2009 #3
    that wasnt given so idk.
  5. Sep 11, 2009 #4


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    It doesn't matter what x is, it should come out the same since we are talking about ratios.
  6. Sep 11, 2009 #5
    ok so how do u get it?
  7. Sep 11, 2009 #6
    If its the same distance, then you just need an average of 42 and 52.


    94/2= 47km/h
  8. Sep 11, 2009 #7
    it's not it. we've tried that. the question is weird. =/
  9. Sep 11, 2009 #8
    Hmm, well if that's the EXACT wording of the question, I have no idea. Sorry.
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