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Homework Help: Physics Help!

  1. Jul 27, 2006 #1
    Hi, I just had a question i had trouble answering, im sure its an easy one, but i cant get it, (since im just starting physics):

    a bus starts at rest and accelerates at 1.5m/s^2 until it reaches a velocity of 9m/s. The bus continues at this velocity and then decelerates at -2m/s^2 until it comes to a stop 400m from its starting point. How much time did the bus take to cover the 400m? (ans: 50 seconds)

    Im using basic velocity and acceleration formulas and I cant get the answer.
  2. jcsd
  3. Jul 27, 2006 #2


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    Gold Member

    show us how you work the problem. Have you ever used latex?
    Last edited: Jul 27, 2006
  4. Jul 27, 2006 #3
    there are three types of movement: the acceleration phase, the movement woth constant velocity and the decceleration.

    1.To calculate the time and distance during the acceleration and decceleration use:

    [tex] a = \frac {\Delta v} {\Delta t}[/tex]

    --> distance at these phases: [tex] s = \bar{v} \cdot t[/tex] with

    [tex] \bar{v} = \frac {1} {2} (v_{2} - v_{1})[/tex]

    2. To calculate the time of the remaining distance with constant velocity use [tex] s = v \cdot t[/tex]

    3. Then sum the calculated times to get to the answer: [tex] t = t_{acc} + t_{cst. v} + t_{dec}[/tex]
    Last edited: Jul 27, 2006
  5. Jul 27, 2006 #4


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    Alternatively, one could use equations of uniform acceleration.
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