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Homework Help: Static Cling in dryer

  1. Jan 15, 2009 #1
    1. The problem statement, all variables and given/known data

    You are unloading a dryer and want to know the amount of charge that causes staic cling. You immediately take 2 empty soda cans which have a mass of 120 grams each. You tie the cans to the end of a string and hang over a nail in the wall so that the cans each hang 30cm from the nail. You take your shirt from dryer and touch it to the cans which are touching each other. The cans move apart until they hang stationary at an angle of 10 degrees from the vertical. Assuming that there are equal amounts of charge on each can you now calculate the amount of charge transferred from your shirt.

    2. Relevant equations

    Sin 10 = x / 30cm
    F = (kq'q)/r^2

    3. The attempt at a solution

    I found the distance between the cans by doubling the distance from the equation sin 10 = x/ 30. x = 5.21 so total distance between cans is 10.42

    Now I think I shoud find the Force. Then I can solve for q and divide it by 2 for total charge on each can.

    I'm stuck on the force part. Should I try to find tension??
  2. jcsd
  3. Jan 16, 2009 #2
    Draw a free body diagram of one of the cans. The forces acting on one of the cans are gravity, mg, vertically downward, the repulsive electric force F horizontally, and the tension of the string T. So,

    Tcos10 = mg
    Tsin10 = F

    The unknowns are T and F and can be solved for using the above equations. Then use F = (kq'q)/r^2 and solve for q (q' = q in this case).
  4. Jan 17, 2009 #3
    OK Thanks!!
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