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Homework Help: I am lost, how do I find tension of a rope given A and M?

  1. Sep 15, 2015 #1
    1. The problem statement, all variables and given/known data
    A rope is used to lower a 1.1 kg bucket into a well at an acceleration of 1.9 m/s2. Determine the tension in the rope (in Newtons). Assume that air resistance is negligible and the acceleration due to gravity is -9.8 m/s2. Take the positive direction to be upward.

    2. Relevant equations
    Newtons 2nd law, A=Fnet/Mnet
    T= m (g-a)

    3. The attempt at a solution

    -1.9 m/s2 = X/1.1 = -2.09N (wrong)
    1.1 (-9.8-1.9) = -12.9N (Unsure if right/wrong)

    I am lost, I am suppose to use newtons 2nd law equation but it makes no sense, please help.
  2. jcsd
  3. Sep 15, 2015 #2
    Have you drawn a free body diagram? If T is pointing upward and g is pointing downward, what is the net external force on the bucket?
  4. Sep 15, 2015 #3
    I did draw a free body diagram, hopefully correctly. The weight would be pulling it down making the tension to pull up causing the net external force to be 0 since they cancel each other out, right? If I plugged 0 into the equation for the net force then what would I solve for, since there would be no X?
  5. Sep 15, 2015 #4
    Okay, so the tension and weight do not equal each other, instead they add up to equal the net force, correct? Meaning if I use that equation to find the net force, I then add the weight to it to find the tension? Meaning it would be -2.09 + 1.1kg = .99N?
  6. Sep 15, 2015 #5
    Let T be the upward tension, and mg be the downward force of gravity on the bucket (i.e., its weight). The net of these in the upward direction is T-mg. If a is the upward acceleration, what is Newton's second law written in terms of these parameters? In this problem, is "a" positive (upward) or negative (downward)? What does the force balance you wrote down give you for the tension in the rope?

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