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Speed and Acceleration Question

  1. Sep 7, 2008 #1
    A sprinter accelerates to his max speed in 4.0s. He then maintains this speed for the remainder of a 100-m race, finishing with a total time of 9.1s. What is the runner's avg acceleration during the first 4.0s, during the last 5.1s?
    I know that the runner starts at 0-m for his initial position and his final position is 100m. I also know that the acceleration from 4.0s-9.0s is 0 because he keeps the same speed. It seems I still have 2 unknown variables when trying to find the position after 4.0s and velocity for each part of the race.
    100m=X + V(5.1s) Have 2 unknowns here
  2. jcsd
  3. Sep 7, 2008 #2
    X + V(5.1) = 100; good start.

    Now, assuming acceleration a (from 0 to 4 seconds) is constant, you can write both X and V in terms of a and substitute into your equation. a will then be the only unknown in the equation.