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Homework Help: Mechanics: Straight line motion

  1. Oct 28, 2012 #1
    1. A car is sitting at a stop light and then accelerates from rest when the light turns green.The acceleration of the car is a combination of forward acceleration but also slowing down due to drag forces.The final total accelaration of the car has the form a(t)=b/(t+T)^3 with constants b=2000 m s and T=10s
    a) What are the cars velocity and position as a function of time?
    b) What are the car's velocity and position at t=5.0 s?

    Attempt to a solution. I calculated integral of the acceleration function and got v(t)=b/[-2*(t+T)^2] and x(t)=b/[2(t+T)] However it doesnt coincide with what the teacher has got in his answer.I got 4.44m/s and 66.6 m as answerst to b) part.Did I make a mistake anywhere,the problem must be trivial,but I am afraid I am doing something wrong.Can anyone help me please?
  2. jcsd
  3. Oct 28, 2012 #2

    Doc Al

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    Staff: Mentor

    What's the velocity at t = 0? (I think you forgot to consider the constant of integration.)
  4. Oct 28, 2012 #3
    True! then I get constant as b/[-2T^2]. Thank you! (Since car is initially at rest I assume v(0)=0)
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