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Homework Help: Acceleration and distance travelled questions

  1. Apr 15, 2010 #1
    1. The problem statement, all variables and given/known data[/b
    a car traveling at 36km/h accelerates to 78km/h in 6 seconds. the brakes are applied and the car stops in a distance of 120m, draw a v/t graph and workout

    The rate of acceleration? i got 6km/h please correct if this is incorrect
    The distance travelled during the acceleration stage?
    The time to stop the car?
    If the car has a mass of 900kg. determine the increase in kinetic energy?

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Apr 15, 2010 #2
    How about providing some of those equations? If you do that you'll be nearly done solving the problem.

    Note that the units of acceleration are displacement/time^2. By how much does the velocity change per second? You accelerate from 36 km/h to 78 km/h in 6 seconds, so you can solve that easily.

    If you draw the velocity curve over time, the area below it represents distance traveled, and the slop at any instance represents acceleration.

    Else, there are three equations relating displacement, velocity, and acceleration. Those will answer the whole problem except the one about kinetic energy. You can look up that equation also.

    "Increase" of KE implies two measurements at different times. Those could be from 36 to 78, from 78 to 0 or from 36 to 0. The latter two cases will yield a negative result.
  4. Apr 15, 2010 #3
    for your solution of acceleration, you are numerically close, but still not quite correct
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