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Constant Velocity Problem

  1. Sep 11, 2009 #1
    This is probably very simple, but it's causing me problems. I keep coming up with VERY unrealistic times. Any help would be greatly appreciated!

    One simple model for a person running the 100 m dash is to assume the sprinter runs with constant acceleration until reaching top speed, then maintains that speed through the finish line.
    If a sprinter reaches his top speed of 11.3 m/s in 2.54 s, what will be his total time?
     
  2. jcsd
  3. Sep 11, 2009 #2

    Pengwuino

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    Gold Member

    What have you come up with so far?
     
  4. Sep 11, 2009 #3
    Because I have no idea where to start, I keep trying to do it mathematically. Like, 100/11.3 and then adding or subtracting the 2.54 seconds. I also tried drawing it out in a graph. When I did that I found myself in the same place. Not enough information to finish anything! I know that the equation is the change in velocity/change in time.

    I got 4.45m/s^2 for the first velocity, but that doesn't seem right. I just graphed it and used Pythagorean Theorem. That would mean he ran 3.65 m at 4.45m/s^2 before reaching 11.3 m/s^2 for the other 96.35 yards. Then if you try to do Pythagorean Theorem again, it doesn't work. The hypotenuse is 11.3 and the height is 96.35. I am really stuck!
     
  5. Sep 11, 2009 #4

    rl.bhat

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    Displacement = Average velocity x time.
    You know the sprinter's initial velocity and maximum velocity.
    What is the average velocity and displacement?
    Next what is the remaining distance? How much time he takes to run this with the maximum velocity?
     
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