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Homework Help: A basic a, v, t problem?

  1. Mar 3, 2010 #1
    1. The problem statement, all variables and given/known data
    If Carol Ann wakes up and crawls across her bedroom at an aceeleration of 0.45 m/s^2 forward for 1.3s, how fast would she be going after 1.3 seconds if he had started with a velocity of 0.25 m/s forward?

    2. Relevant equations
    d = (v1+v2/2)t
    a = v2 - v1 /t

    3. The attempt at a solution
    so we're looking for V right? Which would be v1 & v2.
    v2 - v1 = at
    = 0.25 x 1.3
    = 0.325

    but the answer here says 0.84 m/s forward.

    What am I doing wrong? Please help, thank you so much.
  2. jcsd
  3. Mar 3, 2010 #2
    The equation you use is right. How you apply it, is not. I don't understand at all what you meant with" we're looking for V right? Which would be v1 & v2.
    v1 is the initial velocity, wich is 0.25 m/s
    v2 is the final velocity, wich is what were after.
    you haven't used the acceleration at all.
  4. Mar 3, 2010 #3
    But what we're looking for is "how fast would she be going after the 1.3 s" isn't that the speed?
  5. Mar 3, 2010 #4


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    Staff Emeritus
    Science Advisor
    Homework Helper

    It is the velocity after the 1.3 s have elapsed, which is v2 in the equation you used. And v1 is the velocity at the beginning of the 1.3 s -- and they tell you what it is in the problem statement. They also tell you what the values of a and t are.

    To summarize:

    v2 - v1 = a t, as you said.

    You are trying to find v2. You are told what everything else in the equation is.
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