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Homework Help: A mail bag with a mass of 105kg is suspended by a vertical rope of length 7.00m .

  1. Oct 21, 2014 #1
    ::A mail bag with a mass of 105 kg is suspended by a vertical rope of length 7.00 m .

    A) What horizontal force is necessary to hold the bag in a position displaced sideways a distance 3.00 m from its initial position?
    Take free fall acceleration to be g = 9.80 m/s2 .

    B) How much work is done by the worker in moving the bag to this position?
    Take free fall acceleration to be g = 9.80 m/s2 .

    m= 105 kg
    y= 7 m
    x= 3 m

    So first I made a right triangle to find the angles, the angles I found were 25(from the vertical) and 66.

    The tension in the string is 105 kg x 9.8 m/s2 right? with that I have T=1029 N

    I then used 1029tan(25)= 479 N .

    What do I need to do to figure out ho much work is done?
    tips for moving on?
    Last edited: Oct 21, 2014
  2. jcsd
  3. Oct 21, 2014 #2
    Work is the integral of the working force over the arc length through which it acts. Have you tried calculating that?
  4. Oct 21, 2014 #3
    For work just take the weight of the object multiplied by its displacement, you'll probably need the angle you calculated above. Also, I think your above calculations are incorrect...
    edit: not incorrect, just not what the problem is asking for
    Last edited: Oct 21, 2014
  5. Oct 21, 2014 #4
    you calculated the tension if the bag was just hanging vertically, I believe you need to calculate tension while the bag is displaced...
  6. Oct 21, 2014 #5
    Ok, after doing this problem it looks like you are on the right track (you've calculated the weight and the angle to the vertical). Your next step will be to use the weight and angle to calculate the tension in the rope, then use this tension (and angle) to calculate the force needed to hold the bag a certain distance from the vertical.
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