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Problem finding net force

  1. Sep 22, 2011 #1
    1. The problem statement, all variables and given/known data

    A flea jumps by exerting a force of 1.20 X 10-5 N straight down on the ground. A breeze blowing on the flea parallel to the ground exerts a force of 0.500 X 10-6 N on the flea. Find the direction and magnitude of the acceleration of the flea if its mass is 6.00 X 10-7 kg. Do not neglect the force of gravity.


    2. Relevant equations

    a= net F / m
    w=mg


    3. The attempt at a solution

    I went ahead and found the weight of the flea by multiplying its mass times gravity (6X10-7)(9.8)= 5.88X10-6 N which I'm assuming will be figured into the net F, but I'm not sure exactly where to go from here. Does weight need to be subtracted from the force of the flea on the ground and the force of the breeze on the flea? or does the weight and the force of the flea need to be subtracted from the force of the breeze? am I on the wrong track all together?? Do I need to somehow break it down into x and y components.. in which case I'm more lost than I thought. :)

    Also, I suppose the weight needs to be figured into the direction? I tried tan-1(.5X10-6/1.2X10-5) for an angle of 2.39o but the answer in the back of the book is 4.68o so obviously I don't know what I'm doing.

    Thank you in advance for any help :)
     
  2. jcsd
  3. Sep 22, 2011 #2

    PhanthomJay

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    The breeze force acts in the x direction, while the weight and ground forces act in the y direction. You have to look at the net forces in the x direction to solve for the acceleration in the x direction, then look at the net force in the y direction to solve for the acceleration in the y direction. Then the acceleration magnitude and direction comes from pythagorus' theorem and basic trig.
     
  4. Sep 22, 2011 #3
    I guess I'm just having problems figuring out how to deconstruct this then. I think I was close to having everything snap into place in my mind, but it's gone. Is this the right idea? netFy= Fflea-w= may... ay= 10.2m/s2? and netFx= Fbreeze= max... ax= .83m/s2?
     
  5. Sep 22, 2011 #4

    PhanthomJay

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    Yes, exactly (I didn't check your numbers, but your equations are correct).. Just be a bit more clear on the direction... Fnety is up....so ay is up..now solve for the mag and direction of a.
     
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