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Homework Help: What net force is acting on the object along the incline?

  1. Mar 11, 2006 #1
    Problem:

    An object of mass 2.0kg starts from rest and slides down an inclined plane 69cm long in 0.90s. What net force is acting on the object along the incline?


    Now, I used what I was given and plugged it in the equation:

    deltaX=1/2at^2 + V0t

    I come up with acceleration = .0552 m/s^2

    I plug this into equation:

    Fnet = ma for a net force of .11N

    This is wrong. Am I missing something? I don't have angle theta to use the equation: mgsin(theta).
     
  2. jcsd
  3. Mar 11, 2006 #2

    What did you do to get that for an acceleration, thats not what I get when I use your equation.
     
  4. Mar 11, 2006 #3
    Your thinking is correct, the only thing is that the acceleration you've calculated isn't the correct value.

    The problem indicates that:

    x= 69 cm = 69 * 10-2 m
    v0= 0 m/s
    t= 0.90 s

    Because v0= 0 m/s the equation deltaX=1/2at^2 + V0t becomes:

    deltaX=1/2at^2

    therefore

    2 delta X= at2 so
    a= 2 delta X/ t2

    Can you get to the right answer now?
     
  5. Mar 11, 2006 #4
    oops, i messed up the easy algebra and put .5t^2 on the denominator instead of multiplying deltaX by two. Such an easy mistake can kill a problem. Thanks for everyones help.
     
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