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Physics 11 Force and potential energy

  1. Dec 20, 2006 #1
    1. The problem statement, all variables and given/known data

    A constant net force of 410N up is applied to a stone that weighs 32N. The upward force is applied through a distance of 2.0m andthe stone is then released. TO what height from the point of release will the stone rise?

    2. Relevant equations

    Ep=mgh

    3. The attempt at a solution

    Ep=mgh
    410=32(h)
    h=13m
     
  2. jcsd
  3. Dec 20, 2006 #2
    I'm not sure where you're going with your solution.
    Personally, I'd apply impulse again to get the stone's final velocity at the time of release, and then treat it as one-dimensional motion with constant acceleration.
     
  4. Dec 20, 2006 #3
    i can't use impulse can I? i don't have a time?
     
  5. Dec 20, 2006 #4
    Picky, picky....:blushing:

    OK, how about the Work-Energy theorem to find the velocity at release?
     
  6. Dec 20, 2006 #5
    Ek=1/2mv^2? and which force do i use
     
  7. Dec 20, 2006 #6
    Ah, no. Can you state the Work-Energy Theorem? (If not, can you look it up in your textbook or notes?)
     
  8. Dec 20, 2006 #7

    cristo

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    Staff Emeritus
    Science Advisor

    An easier way is to use the Work-Energy Theorem, as stated above. Calculate the work done by the force on the stone for the 2m that it is applied (recall, work done = force * distance). When the stone reaches its maximum height, all the energy is the potential energy, so you can equate the potential energy to the work done, and solve for h.
     
    Last edited: Dec 20, 2006
  9. Dec 20, 2006 #8
    Work done on object is equal to the change in its kinetic energy
     
  10. Dec 20, 2006 #9
    OK, so can you apply it? (I know I can...)
     
  11. Dec 20, 2006 #10
    what do i do once i've found velocity
     
  12. Dec 20, 2006 #11
    Use a basic kinematics equation for motion with constant acceleration.
     
  13. Dec 20, 2006 #12
    the answer i got was 26m
     
  14. Dec 20, 2006 #13
    Oddly enough, so do I.
     
  15. Dec 20, 2006 #14
    ok good, thank you very much
     
  16. Dec 20, 2006 #15
    do you have time for another question?
     
  17. Dec 20, 2006 #16
    Not really... but I'm in the middle of studying for my physics final, so this helps me, too. Look, If I don't answer, someone else will. (That's why this forum rocks!)
     
  18. Dec 20, 2006 #17
    ok sounds good, i think im going to make a new topic though
     
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