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Homework Help: Work done by gravity

  1. Nov 12, 2007 #1
    1. ok dont know if this is the right section but here i go. The being asked is compare the work done by gravity to the change in potential energy? There is a system, but thas not important what is important is that the mass is falling at an acceleration of 2.789 m/s squared.

    2. So i found the change in potential by doing mgh final - mga initial. i used the acceleration of 2.789 instead of 9.8 as g though. The when i attempted to find the work done by gravity i dunno if i should use 2.789 or 9.8.

    3. Might sound like a jumple but i have no concrete answer to go upon so this is the best i could do. Basically i wanna know which accelerations i should be using since its all jumbled in my head. I am also aware that W done by the conservative force (gravity in this case) is equal to the negative potential chnage. I just need help getting there
  2. jcsd
  3. Nov 12, 2007 #2
    2) your assumptions were incorrect. mgh is always 9.8 unless you are on a different planet. i would assume that for this problem you just have air drag or something simmilar.
  4. Nov 12, 2007 #3
    so eventhough the mass is falling at a rate of 2.789 m/s squared i must assume that change in potential energy = mgh final - mgh initial (m being mass, g being 9.8, and h being the final and intial height).
  5. Nov 12, 2007 #4
    the acceleration due to gravity is always 9.8 m/s^2, unless you're not on earth. mgh is a fancy way of calculating work by separating force into m and a, which is g, and distance into h, which is the distance parallel to your object, and the one that you should me worrying about.
  6. Nov 12, 2007 #5
    i suppose just seems weird that the potential energy is calculated using gravity instead of the falling acceleration.
  7. Nov 12, 2007 #6
    potential energy is the potential the object has. the force upon it times the distance it can move.
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