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Question wording, please confirm

  1. Feb 17, 2007 #1
    bascially, i'm 100% sure i understod the wording of the question, below, can you please check though i confirm i interpretted right, thnx buddies

    1. The problem statement, all variables and given/known data

    the kinetic energy, E joules, of an object moving with a speed v m/s, is directly proportional to v^2.

    the kinetic energy of the object is 15 480 joules when its speed is 6 m/s.

    a) find a formula for E in terms of v

    2. Relevant equations

    none

    3. The attempt at a solution

    Ev (proportional sign) v^2
    Ev = kv^2
    15480 x 6 = k x 6^2
    92 880 = k x 36
    k = 2580

    Ev = 2580 x v^2
    E = 2580v




    thnx for the help
     
  2. jcsd
  3. Feb 17, 2007 #2

    Hootenanny

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    I am curious as to how you came to this conclusion;
     
  4. Feb 17, 2007 #3
    that where i get confused, i kinda thought the question meant that the kin energy times the speed is proportional to the speed squared

    either that or i'm totally confused

    please help

    thnx
     
  5. Feb 17, 2007 #4

    Hootenanny

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    No, not quite. The statement means simply that [itex]E\propto v^2[/itex].
     
    Last edited: Feb 17, 2007
  6. Feb 17, 2007 #5
    o rite, i see, thnx for clearing that up, but isn't it E proptional to v squared?

    thnx buddy
     
  7. Feb 17, 2007 #6

    Gokul43201

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    The trick (if I understand the source of your confusion) is to learn to partition the sentence correctly.
    Try to throw away all non-essential details and extract the thrust of the statement, i.e., some property of some object is proportional to some other property.

    Then you can keep track of the details separately...
    Some property = KE
    some object = "object moving with a speed v"
    some other property = v^2

    The upshot of this is that one property is proportional to another, namely, KE prop v^2

    Perhaps it would help if you read the sentence as though it were written this way: the kinetic energy, E joules, (of an object moving with a speed v m/s) is directly proportional to v^2.
     
  8. Feb 17, 2007 #7

    Hootenanny

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    Sorry, that was a typo. Now corrected :smile:
     
  9. Feb 17, 2007 #8

    o rite eyh that'll be where i was going wrong lol, thnx for that, i understadn now :D
     
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