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Homework Help: I have a question I need help with (acceleration)

  1. Jun 25, 2004 #1
    I have a question I need help with

    I am having trouble figuring out what to do with this problem. Can anyone help?



    An automobile starts from rest and accelerates to a final velocity in two stages along a straight road.Each stage occupies the same time. In stage 1, the magnitude of the car's acceleration is 3.0 m/s^2. The magnitude of the car's velocity at the end of stage 2 is 2.5 times greater than it is at the end of stage 1. Find the magnitude of the acceleration in stage 2.
     
  2. jcsd
  3. Jun 25, 2004 #2
    2.5*(3t) = 3t + a * (t)
    7.5t - 3t = at
    4.5t = at
    a = 4.5

    wow, i hope i didn't make any mistakes.

    edit: i did lol, too late for me. such sillyness. (rechecks my stats homework)
     
    Last edited: Jun 25, 2004
  4. Jun 25, 2004 #3
    Stage one:
    V = ?, u = 0, a = 3ms^-2, t=t
    v=u+at
    ?=3t

    Velocity at end = 2.5(3t) = 7.5T

    Stage two:
    U = 3t, V = 7.5t, a = ?, t=t
    v = u + at
    7.5t = 3t + at
    divide through by t
    7.5=3+a
    a=7.5-3
    a=4.5ms^-2

    Where U = speed at the beggining of the stage, V = Final speed, T = time, a = acceleration.
    Kinematics is fun, don't be afraid to leave things as unknowns in algebraic form if you have to compile information in two stages. A lot of examination 'proof' questions will ask for this.
     
    Last edited: Jun 25, 2004
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