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Tension and Normal Force

  1. Oct 21, 2009 #1
    A 5.0 kg mass is suspended by a string from the ceiling of an elevator that
    is moving upward with a speed which is decreasing at a constant rate of 2.0
    m/s in each second. What is the tension in the string supporting the mass?

    -I know that the Normal Force on the string is Fn=mg so it would be equal to 49 N, however how would I use the rest of the information to calculate the tension in the string. I know that the answer is supposed to be 39 N but I don't know how to approach it from this point.
  2. jcsd
  3. Oct 21, 2009 #2
    2.0 m/s/s means that there is an additional force caused by the deceleration of the elevator (negative acceleration), and F=ma. Therefore f_total = 49N - 5kg*(2m/s^2) = 39N
  4. Oct 21, 2009 #3
    okk that's what I was thinking but I felt as if it was just a guess that happened to work out thanks for the explanation
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