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Friction problem. Help Please?

  1. Jan 19, 2009 #1
    1. The problem statement, all variables and given/known data
    A wounded soldier caught in Line of fire is pulled away by his comrade with a force of 70lbs at 65 degrees. The wounded solider(with his gear) weighs 180 lbs and the coefficient of friction between him and ground is .55
    How quickly will he be accelerated out of harms way?

    2. Relevant equations
    u=coefficent of friction
    f=uF, w=mg, F-f=ma

    3. The attempt at a solution


    I dont know what to do(correctly) after this. Have I done anything wrong in the steps shown above?
  2. jcsd
  3. Jan 20, 2009 #2


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    Homework Helper

    There are two components to the force applied.

    The vertical component lessens the frictional load.
    The horizontal component is what you will have offset by the frictional drag.

    Personally I would convert straight away to SI units.

    1 lb force = 4.448 N
  4. Jan 20, 2009 #3
    Our teacher wants us to keep the values like I have put there though. What should I do after finding the friction?
    Do I use F-f=ma? If I do this, the answer I get is -6.176 ft/s(squared). So that means that he wont be accelerated away right?
  5. Jan 20, 2009 #4


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    Homework Helper

    If the horizontal component of the applied force is less than the maximum needed to overcome friction ... then whoever is doing the pulling should seek shelter.
  6. Jan 20, 2009 #5
    Ok thank you!
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