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Homework Help: Walking up a hill physics work

  1. Nov 10, 2005 #1
    A man is carrying a bag that weighs 10 kg. He's walking up a hill, when he stops he is 10 vertical meters higher. g = 9,8. I now have to find the work that's been done on the bag. I have W = m*g*d
    How do I find d?
  2. jcsd
  3. Nov 10, 2005 #2
    d is the displacement against the force of gravity. Gravity acts in the vertical direction.

    I recommend you actually learn what the letters really mean instead of just plugging things into formulas.
  4. Nov 10, 2005 #3


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    you mean that its mass is 10kg?
    in the work equation, you have to find the distance in the direction of the force.
  5. Nov 10, 2005 #4
    yes it's mass is 10kg. I know what displacement is, but he's not just moving in the vertical, but also the horizontal. His start coordinates are (0,0) and at the end (?,10). Surely it's not only the vertical displacement that I have to find? Or am I wrong?
  6. Nov 10, 2005 #5
    It says
    10 VERTICAL meters higher, start = (x1,y), end = (x2,y+10)
  7. Nov 10, 2005 #6


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    Is there any resistance in the horizontal displacement. Is a force needed to move in that direction? You only need the distance in the direction of the applied force.
  8. Nov 10, 2005 #7
    Ok, so the horizontal displacement does not count here? The work done by the man on the bag is the same as the work done by gravity on the bag?
    Thanks for taking the time to help me.

    No, there's no friction. I asked because he's walking upwards with an angle. But if I only need the vertical displacement, then it's piece of cake.
  9. Nov 10, 2005 #8


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    The Work done by the man is POSITIVE,
    since the Force by the man is in the SAME sense of direction as the motion.
    The Work done by gravity is NEGATIVE,
    since gravity is in the OPPOSITE sense of diraction as the motion.

    Only the Force component PARALLEL to the motion does any Work. or,
    Work is only done thru the displacement component PARALLEL to the Force.
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