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Why acceleration is not 9.8m/s^2?

  1. Feb 2, 2013 #1
    1. The problem statement, all variables and given/known data

    An object is dropped from ret from a height of 39.4m. What is its average acceleration (assumed to be constant) if it hits the ground with a speed of 1.61m/s?


    2. Relevant equations



    3. The attempt at a solution

    I actually got the answer from this question. But I am wondering why a is not -9.8m/s^2
    The answer is 3.29×10-2 m/s^2, shouldn't it be negative as acceleration is acting downwards?
     
  2. jcsd
  3. Feb 2, 2013 #2

    mfb

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    2016 Award

    Staff: Mentor

    Possible reasons:
    - The object is not dropped on earth, but somewhere else
    - Some other force acts on it

    The sign of the acceleration is arbitrary and depends on the coordinate system.
     
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