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Homework Help: Force of friction

  1. Nov 6, 2004 #1
    i need any help that anyone can give me... i understand some things in physics, but i don't get the big picture, and I am really not sure of how to do things, and i am really confused about this one problem in particular...

    it states: a tractor uses a chain to drag a 675kg tree along the ground at a constant speed. The chain makes an anlge of 37degrees with the ground. What is the tension of the chain if the coefficient of kinetic friction between the ground and the tree is .45?

    my teacher emailed me the answer of t=2785 N, but i don't understand how he got the answer. Could someone explain this to me, and tell me what I am doing wrong please???
  2. jcsd
  3. Nov 6, 2004 #2


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    Gold Member

    Well, the best way to tell you what you are doing wrong is for you to explain what you've done. I'll try to give you a general idea of the steps; if you need more help, just ask (and give specifics on where you're stuck).

    The first thing you should do is draw a free body diagram. You are told that the tree moves with a constant velocity so you know it is not accelerating --> therefore the net force on the tree is 0. What are the forces acting on the tree?
    - its weight
    - the tension
    - the friction

    If you break the problem down into horizontal and vertical components, you will have two equations to solve: the weight will be balanced by the vertical component of the tension (1 equation) and the friction will be balanced by the horizontal component of the tension (the other equation). Remember that the friction is a function of the normal force on the tree (f = μN), which is not equal to the weight in this problem (see your first equation).

    Well, that ought to get you going. I hope that helped.
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