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Seemingly simple mechanics questions

  1. Mar 11, 2016 #1
    1. The problem statement, all variables and given/known data
    The problem basically states that there is a box with weight mg and a string that is less of magnitude with tension t as shown in this picture: https://gyazo.com/efeb48469cfb44399bea6c2dcc9e87c7
    The question is what are two possibilities for this situation and the answers are : rising with a decreasing speed and falling with an increasing speed. I do not understand the rising with a decreasing speed aspect of it in conceptual and mathematical terms. How does this happen (in what scenario for example)?


    2. Relevant equations:
    F=ma, mg etc.



    3. The attempt at a solution
    It's obvious that acceleration is negative from the start as mg has the greater magnitude (T-mg/m = a)
    my thought was we either have an initial tension that decreases of some sort or we have an initial velocity above 0 for the box and it decreases as time goes on
     
  2. jcsd
  3. Mar 11, 2016 #2

    haruspex

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    Do not assume the system was previously at rest, with only mg and T<mg acting on it since. The object may have been given an initial speed by some some larger T, or by some other means.
     
  4. Mar 13, 2016 #3
    That problems seems somewhat unspecific

    I can think of scenarios in which at least the last two answers apply and possible the first two as well

    I am curious as to what the answer is and why
     
  5. Mar 13, 2016 #4

    haruspex

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    Note the constraint mentioned here:
     
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