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Homework Help: Distance calculated from Energy

  1. Dec 8, 2011 #1
    122yhw3.jpg

    Please help me with part b, thank you!
     
  2. jcsd
  3. Dec 8, 2011 #2

    Simon Bridge

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    Complete the following so the sentences are true:

    The particle starts with ________J kinetic energy.
    Work done on the particle increases/decreases it's kinetic energy.

    Now how is the Work related to the distance the particle travels?

    To help you properly, really need to see your working.
     
  4. Dec 8, 2011 #3
    The particle starts with 0 J kinetic energy.

    Force relates the work to the distance the particle travels.
     
  5. Dec 8, 2011 #4

    Simon Bridge

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    Doesn't the particle have some initial velocity?

    Select "increases" or "decreases" for the second sentence.
     
  6. Dec 8, 2011 #5
    Well, at x=0, the Force is 2 Newtons but the x is 0, so wouldn't 2N * 0m = 0 J?

    Work done on the particle increases it's kinetic energy.
     
  7. Dec 8, 2011 #6

    Simon Bridge

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    OK - you've forgotten about the initial velocity. When I read part (b) I see this:

    (b) if it starts with a velocity of 2m/s in the +x direction, how far will the particle go in that direction before stopping?

    Thus - how much kinetic energy is it starting with?
     
  8. Dec 8, 2011 #7
    Ooh okay, it's 1 J.
     
  9. Dec 8, 2011 #8

    Simon Bridge

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    No worries - the eye sometimes skips part of a question. Hate it when that happens :)
     
  10. Dec 8, 2011 #9
    Thanks :] So once I have 1 J, how do I solve for the distance? I added 1 J to the 3 J at x = 4. W = fd so.. 4 J = F d. What would be my F?
     
  11. Dec 8, 2011 #10

    Simon Bridge

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    You don't need F. Look at your graph. You did it correctly when you thought you started with 0J energy - do the same thing only starting with 1J

    So - you start with 1J
    In the first meter moved, you gain 1J (area under F-x graph) for a total of 2J
    What happens in the next meter moved?
    How far before you've lost all the KE?
     
  12. Dec 8, 2011 #11
    2.5m! Thanks so much, I really appreciate your help :)
     
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