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Accelerated motion problem

  1. Oct 28, 2009 #1
    1. The problem statement, all variables and given/known data
    A driver slows her car from 33.5 km/hr at a constant rate of 0.29 m/s2 just by taking her foot of the accelerator (the "gas" pedal). Calculate the distance the car travels during the fifth second that she is coasting.


    2. Relevant equations



    3. The attempt at a solution
    I am doing something wrong b/c I get 42.905m, but I know that is wrong.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 28, 2009 #2

    danago

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    Gold Member

    How are you arriving at that answer? If you post your steps then someone can show you where you went wrong.
     
  4. Oct 28, 2009 #3
    Use your kinematics.

    You know the following:

    vi = 33.5 km/hr
    a = -0.29 m/s2

    "During the fifth second" means you start at 4 seconds and end an instant before the 5th second. So, you need to find the [tex]\Delta[/tex]x at t = 4 and t = 5.

    Now, what you do with that knowledge is up to you. I probably told you too much as it is.

    Good luck!
     
    Last edited: Oct 28, 2009
  5. Oct 28, 2009 #4
    initial velocity = 9.306m/s
    acceleration = -.29m/s/s
    time = 5s
    displacement = x

    x = initial velocity *time + 1/2at*t
    x = 42.905m
     
  6. Oct 28, 2009 #5
    Okay, all you found was how far it went in the FIRST FIVE seconds. The question (at least the way your worded it) wants to know how far it goes DURING THE FIFTH second. Do you see the difference? Refer to my previous post if you are confused. If you are still confused after reading that, let us know!
     
  7. Oct 28, 2009 #6

    danago

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    Gold Member

    Would that not be during the 6th second? From 0s to 1s would be the first second, 1s to 2s is the second second etc., So the 5th second should be from 4s to 5s?
     
  8. Oct 28, 2009 #7
    Yeah, I'm an idiot. Thank you. The idea was right, I just confused myself. Whoops!

    Thanks for the correction. I fixed it.
     
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