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How to solve for Initial velocity Problem

  1. May 22, 2016 #1
    1. The problem statement, all variables and given/known data
    A bobsled glides down a hill with an acceleration of -4.5 m/s If it stops after 5 s, what was its initial velocity?

    2. Relevant equations

    i know vf(final)= v + at

    3. The attempt at a solution
    i multiplied -4.5m/s by 5s and i got the correct answer the only problem is the answer is negative, i need it to be positive. Where or what did i do wrong?
     
  2. jcsd
  3. May 22, 2016 #2

    NascentOxygen

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    Staff: Mentor

    Write the equation you are using to solve this problem, then substitute in it for the variables you know.
     
  4. May 22, 2016 #3
    The issue is I do not know what equation to use. I though the initial velocity equation would help, but I am not given final velocity I only have two known variables
     
  5. May 22, 2016 #4

    NascentOxygen

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    Staff: Mentor

    The problem states clearly what the sled's final speed is. The unknown here is its initial speed.
     
  6. May 22, 2016 #5
    so distance over time ?

    i know the equation for for final velocity is vf= v(initial) + (a)(t)<---- acceleration multiplied by time

    to get the final velocity i did do distance over time giving me -0.9 then i multiplied -4.5m/s by 5s i added all those figures together giving me a number that is not similar to the answer key
     
  7. May 22, 2016 #6

    NascentOxygen

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    Staff: Mentor

    The sled is brought to a stop, which tells you its final speed is 0 m/s.
     
  8. May 22, 2016 #7
    o damn, right under my nose.
     
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