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Homework Help: Velocity Problem

  1. Mar 6, 2008 #1
    1. The problem statement, all variables and given/known data
    A car is traveling along a straight road at a velocity of +31.0 m/s when its engine cuts out. For the next ten seconds, the car slows down, and its average acceleration is a1. For the next five seconds, the car slows down further, and its average acceleration is a2. The velocity at the end of the fifteen-second period is +24.5 m/s. The ratio of the average acceleration values is a1/a2 = 1.67. Find the velocity of the car at the end of the initial ten-second interval.

    2. Relevant equations
    VF = V0 + at

    VF = Final velocity
    V0 = Initial velocity
    a = acceleration
    t = time

    3. The attempt at a solution

    The answer is +26 m/s, but I don't know how to get it...

    24.5 = 31.0 + a2(15)

    a2 = -13/30 = -4.333...
    a1 = -3.8534

    VF = 31.0 + (-3.8534)(10)
    VF = -7.534
    Last edited: Mar 6, 2008
  2. jcsd
  3. Mar 7, 2008 #2
    Ok, do you know that you can find the average acceleration just by doing simple operations with the inidial velocity and the final velocity?

    And with that you can find the values of a1 and a2 through use of simultaneous equations. You should be able to solve from here.
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