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Homework Help: Upward vertical Force problem

  1. Sep 26, 2007 #1
    can anyone help me start this problem?

    Besides its weight, a 2.8 kg object is subjected to one other constant force. The object starts from rest and in 1.2s experieces a displacement of (4.2i - 3.3j) m, where the direction of j is the upward vertical direction. determine the other force
  2. jcsd
  3. Sep 26, 2007 #2


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    Start by splitting the displacement into i and j components. Using the displacements calculate the total force on the object. Then subtract the weight force from the total force to get the 'other force'.
  4. Sep 26, 2007 #3
    kk, I got...

    deltaX = Vixt + 1/2at^2

    4.2 = 0 1/2a(1.2)^2

    a = 5.8i

    deltaY = Viyt + 1/2at^2

    -3.3 = 0 + 1/2a(1.2)^2

    Y = -5.4j

    F = 2.8kg(5.8i + 5.4j) ?
  5. Sep 26, 2007 #4


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    Seems roughly ok. I don't have to check your arithmetic, right? But aren't you losing signs again in the total force? Shouldn't the y component of the force be DOWN?
    Last edited: Sep 26, 2007
  6. Sep 26, 2007 #5
    yup yup! you're right again, dick. Signs are always messing me up. Thanks again.
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