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Homework Help: Linear Dynamics Help: friction and horizontal force

  1. Oct 7, 2013 #1
    1. The problem statement, all variables and given/known data
    I've been having some problems trying to do a few lab questions for my physics class, I'm not very good at it but I do try to make the best of it so anyone that's willing to help me give me any pointers would be awesome. I have two physics problem and I'm supposed to do them online and I've provided snapshots of them as well:

    1. A three-picket fence of mass 422 grams is pulled by a constant force of 0.667 N on a rough surface as shown in the animation. Find the magnitude of the force of friction in Newtons.

    2. A three-picket fence is pulled by a constant-force spring over a horizontal frictionless surface as shown in the animation. The mass of glider + fence is 563 grams and the hanging mass is 49.5 grams. Find the magnitude of the horizontal force exerted by the pulling hand in Newtons.

    2. Relevant equations
    For (1) I know the equation for force of friction =μN and N=mg but I'm not sure how to obtain "μ" based on the animation provided.

    For (2) The net force on the hanging mass would be T-m2g=m2a and the hands that's pulling the glider and fence would be T=m1a, since the force that's pulling it is Tension.
    So, the a=m2/(m1+m2)g, so once we found the acceleration we can plug in the "a" to F=m1a, to find the horizontal force?

    I have attached the pictures in this thread for better visualization as well. The picture shown that the glider have already passed the photogate, thus it shows the the gate time on it.

    Attached Files:

    Last edited: Oct 7, 2013
  2. jcsd
  3. Oct 7, 2013 #2


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    Staff: Mentor

    Hi Solemony. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

    I think we are expected to be able to determine the body's acceleration, so we need some data from the animation. I guess we can't see it playing? So what are those 3 times listed?
    Last edited by a moderator: May 6, 2017
  4. Oct 7, 2013 #3

    The times listed are:

    The fence starts at rest from 12cm from a photogate and each gap/picket is 2cm wide.
    Last edited by a moderator: May 6, 2017
  5. Oct 7, 2013 #4


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    Staff: Mentor

    Can you explain what useful information that data conveys?
    Last edited: Oct 7, 2013
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