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Homework Help: Problem with choosing which axis should be positive or negat

  1. Mar 6, 2016 #1
    1. The problem statement, all variables and given/known data
    A 14.0kg bucket is lowered vertically by a rope in which there is 163N of tension at a given instant. What is the acceleration of the bucket.

    2. Relevant equations
    ƩF = may

    3. The attempt at a solution
    I know how to solve this but I got it wrong because of the signs.
    Since the bucket was being lowered I thought that downward was going to be positive, but the correct solution says that up is positive; WHY?
  2. jcsd
  3. Mar 6, 2016 #2
    It doesn't matter what you choose to be positive or negative. If you chose differently than the book, then your signs will be opposite at the end. That's it. As long as you're consistent, it'll be the same.
  4. Mar 6, 2016 #3
    so even though its negative it's correct? or are you saying i wasnt consistent with my signs and that regardless of what i choose to be positive or negative that as long as im consistent with it that i should get the correct answer?
  5. Mar 6, 2016 #4
    If your answer is the negative of the correct answer, and you chose opposite axes as the correct answer, then your answer is also right. Yes, you can choose your positive direction to be whatever direction you want as long as it stays the same throughout the problem.

    You'll get the correct answer for those axes. If you chose your positive direction to be the opposite direction as someone else, that just means your answer will be the negative of theirs.
  6. Mar 6, 2016 #5
    ohh ok thank you so much!
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