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Homework Help: Force and Work

  1. May 31, 2008 #1
    1. The problem statement, all variables and given/known data

    Our teacher made an unconvincing argument based on this example:
    If a horizontal force of 15 N were a applied to a 2 kg block, and the work done was 20 J, what distance did the object move?

    2. The attempt at a solution
    Using W=F*d the teacher solved this: 20 J=15 N*x -> x=4/3 m.
    This implied that if I applied 15 N to an object of any mass and did 20 J of work, the distance I could move the object is always the same. There seems to be something fundamentally wrong with this statement. But I'm not seeing what it is, I know it's there - I'm think that somehow I need to do something with the weight of the object. I mean if it were to be realistic I would have to calculate friction and gravity too...

    Can somebody please tell me what I missed out?
     
  2. jcsd
  3. May 31, 2008 #2
    That's correct.

    Usually we neglect friction and the gravity doesn't play a role here because this is a horizontal motion.
     
  4. May 31, 2008 #3
    it's more like a resultant force of 15N which moves the body 4/3 m when 20 J of work is done. the 15 N resultant force may include the force you apply - any resistive forces for example.
     
  5. May 31, 2008 #4
    Oh I see what you're saying, I guess my teacher didn't convey that point very well^^
     
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