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Homework Help: Velocity and acceleration

  1. Feb 24, 2012 #1

    Would somebody be able to explain to me how to calculate the answer to this question? I'm studying for an exam and cannot figure it out.


    The rear of a bicycle passes a point O on a road with a velocity 4 ms-1 and an acceleration of 2 ms-2. Four seconds later the front of a car passes O with a velocity of 2 ms-1 and acceleration of 4 ms-2. When and how far from O does the front of the car meet the rear of the bicycle?

    Many thanks

  2. jcsd
  3. Feb 24, 2012 #2


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    You will need to show us some of your thoughts and effort before we can help.
  4. Feb 24, 2012 #3

    This is what I think, but I can't seem to get the correct answer.

    s1 = 4t + 0.5(2)t^2 distance bike goes
    s2 = 2(t-4) + 0.5(4)(t-4)^2 distance car goes

    then set s1 = s2 and solve

    the answer is 16.5 seconds but I can't get this. maybe it is my algebra!

    Thank you
  5. Feb 24, 2012 #4


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    That's the correct method.

    Show how you solve for t.
  6. Feb 24, 2012 #5
    I solved it and got the correct answer.

    Originally I was using (t+4)

    Could you explain to me why it is (t-4) and not (t+4)? What is reasoning behind it?

    Thank you
  7. Feb 24, 2012 #6
    It depends on for which motion do you take the time to be ' t '. See how does it make a difference?
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