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Homework Help: Time question 9

  1. Jan 21, 2007 #1
    1. The problem statement, all variables and given/known data
    How long will it take a mass to accelerate from 30.0m/s (south) to 50.0m/s(north) if its acceleration isa sonstant 4.0m/s2(north)


    2. Relevant equations
    displacement=V/Time
    Aav=V/time
    3. The attempt at a solution
    a=4.0ms2
    v=20ms
    d=Vav*time
    time=v/acceleration
    20ms/4.0ms2
    =time is 5s
     
  2. jcsd
  3. Jan 21, 2007 #2

    cristo

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    Staff Emeritus
    Science Advisor

    No, you have the correct equation, but your change in velocity is incorrect. At the beginning, the mass is moving 30 m/s south and we want it to accelerate and reach 50m/s north. Remember that velocity is a vector.
     
  4. Jan 21, 2007 #3
    i think u can use this simple formula whcih is
    time= change in velocity (vf-vi)/ acceleration
    and remember south and north are oppostite directions *hint*
     
    Last edited: Jan 21, 2007
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