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Homework Help: Terminal velocity of a coffee filter

  1. Oct 11, 2007 #1
    1. The problem statement, all variables and given/known data

    You drop a single coffee filter of mass 1.2 grams from a very tall building, and it takes 47 seconds to reach the ground. In a small fraction of that time the coffee filter reached terminal speed.

    (a) What was the upward force of the air resistance while the coffee filter was falling at terminal speed?

    (b) Next you drop a stack of 6 of these coffee filters. What was the upward force of the air resistance while this stack of coffee filter was falling at terminal speed?

    (c) Again assuming again that the stack reaches terminal speed very quickly, about how long will the stack of coffee filters take to hit the ground?

    2. Relevant equations


    3. The attempt at a solution

    I got the first two parts by setting Fair=mg since these forces are equal in magnitude once terminal velocity is reached (zero net force) but I am seriously stumped on the third part. I thought about the drag equation but I don't see how it's possible to use that with the amount of information I have.
  2. jcsd
  3. Oct 11, 2007 #2


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