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Force applied at an angle to a box?

  1. Oct 29, 2009 #1
    1. The problem statement, all variables and given/known data
    A net force of 4N to the right is applied to a box of 6kg while moving it a distance of 3m to the right.
    (1)How much work is done on the box?
    (2)What if the force is applied at a 30 degree angle above horizontal?


    2. Relevant equations
    (1) W=Fdcos(angle)
    (2) F=ma
    (3) W=Kf-Ki=((1/2)mv^2)-((1/2)mv^2)

    3. The attempt at a solution
    For the first question, to find the work done on the box, I plugged numbers into equation (1).
    W=(4N)(3m)cos(0)
    Cos(0)=1, W=12J

    I don't even know where to begin for question (2). It seems to me that, in order to caclulate Force, I need the acceleration to plug into equation 2, or I need velocities to calculate work in equation (3). I have neither, and I can't think of any other applicable equations. I assumed friction was negligable since it was not mentioned.
     
  2. jcsd
  3. Oct 29, 2009 #2
    why wouldn't plugging numbers in equation 2 work here as well? You already have the force.
     
  4. Oct 29, 2009 #3
    Okay, I feel crazy. I got work and force mixed up and what the questions were asking mixed up. I feel dumb.

    So, equation (1) is used for both questions. The force is the same, the distance is the same, the only thing that changes is the angle.

    Thanks.
     
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