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question regarding kinematics

Discussion in 'MCAT Study Question Q&A' started by ssjsike, Jul 25, 2011.

  1. ssjsike

    5+ Year Member

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    Hi guys, I realize that this is a silly question, but here goes:

    How long would it take an object starting from rest and accelerating uniformly at 1.5 m/s^2 to travel 3 m?

    The answer is 2 seconds.

    I understand the method of using a big 5 kinematics equation (x=vit+.5at^2), but why is this methodology wrong:?

    a=v/t
    d=vt --> v = d/t

    a = (d/t)/t --> a = d/t^2 ---> t = 1.4 seconds

    Thanks for the help everyone!
     
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  3. Temperature101

    Temperature101 Membership Revoked
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    I think you fail to realize that the d= vt is that they using the average velocity. Since the initial velocity is zero, the average velocity is v/2. Then d = (v/2)*t , which is the same as v = 2d/t; replace that in the a= v/t will yield a = 2d/t^2 and t^2= 2d/a....t^2 = 6/1.5 and t = 2. Hope it makes sense...
     
    #2 Temperature101, Jul 25, 2011
    Last edited: Jul 25, 2011
  4. ssjsike

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    Thank you Temperature101! This definitely makes sense.
     

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