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Word Problem.Is this correct?

  1. Feb 21, 2009 #1
    ....got it....

    Thnx though!
    Last edited: Feb 22, 2009
  2. jcsd
  3. Feb 22, 2009 #2
    Check this out.

    x: person's x position
    y: person's y position
    X: raptor's x position
    Y: raptor's y position

    x = 5(sqrt2) (t+3)
    y = 5(sqrt2) (t+3)

    X = 12(sqrt2) t_x
    Y = 12(sqrt2) t_y

    If the raptor wants to catch you, t_x must equal t_y... because the person is on the line x=y and the raptor starts at the origin. So t_x equals t_y equals t.

    Let T represent the time the raptor catches you (with t = 0 being when the raptor starts running). Then we must have that

    5(sqrt2)(T+3) = 12(sqrt2)(T/2)

    The equation is the same for y.

    Solving for T...

    5T + 15 = 6T

    T = 15.

    So it takes the raptor 15 seconds to catch the dude.

    It can't very well be 1.5 s, can it? The raptor has only moved 22.5(sqrt2) = 32 total, while the person has moved 45 total. Even if the raptor was chasing the guy directly, he wouldn't catch him.
  4. Feb 22, 2009 #3
    Comparing my solution with yours(the one that i did after my first post), i see that we have the same idea, in general terms with some slight differences, besides that you have a typo on your solution, because the speed of the raptor is 15sqrt{2}m/s and not 12sqrt{2}m/s so the final answer should be 6 s.

  5. Feb 22, 2009 #4


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    Dearly Missed

    What happened? Did the raptor eat your post instead of you??
  6. Feb 22, 2009 #5
    It looks like that's the case.

    Well, in fact, after i initially posted the problem and the 'solution', after a few hours i wanted to edit it since i found the correct solution, but while tring to post it the pf was having trouble or don't know what, so that's what was left from my post.
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