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Quick Acceleration Problem

  1. Sep 26, 2013 #1
    1. The problem statement, all variables and given/known data

    An object takes 1.20 seconds to reach a velocity of 12.6 m/s. What is its acceleration if it covered 11.34 meters?

    2. Relevant equations

    Vf ^2 = Vi ^ 2 + 2ad

    3. The attempt at a solution

    Well, I am not sure if the initial velocity is zero or if it is starting at some velocity x.

    My attempt:

    12.6^2 = 0^2 + 2(a)(11.34)

    a = 7 m/s^2

    I know this is wrong but I don't understand how to solve it if I don't know what the initial velocity is?

    Thank you.
     
  2. jcsd
  3. Sep 26, 2013 #2
    I would be really glad if someone could quickly explain this to me because I am having a hard time with acceleration problems. Thank you.
     
  4. Sep 26, 2013 #3

    gneill

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    Staff: Mentor

    Looks like you'll need to solve more than one equation. Write separate equations for the distance covered and the final velocity given that there is an initial velocity. Two equations, two unknowns. You only need to find one of them (a).
     
  5. Sep 26, 2013 #4
    12.6 ^2 = Vi ^2 + (2)(a)(11.34)

    12.6 = Vi + a (1.2 seconds)

    After substituting Vi from equation 2 into equation number 1, I find that the acceleration is 4.25m/s/s.

    THANK YOU THANK YOU THANK YOU.
     
  6. Sep 26, 2013 #5

    gneill

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    Staff: Mentor

    Maybe a typo, but check your acceleration value. 4.25?
     
  7. Sep 26, 2013 #6
    Woops. It's 5.25 m/s/s.
     
  8. Sep 26, 2013 #7
    a=v/t with that you have the time then plug it into another equation.
     
  9. Sep 26, 2013 #8

    gneill

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    Staff: Mentor

    :approve:
     
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