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How much work is required to stop an electron

  1. Jun 23, 2015 #1
    1. The problem statement, all variables and given/known data

    How much work is required to stop an electron (m=9.11×10−31kg) which is moving with a speed of 1.40×10^6 m/s ?

    2. Relevant equations



    3. The attempt at a solution

    E.g a particle has KE=10J. The work that must be done on it to stop it is -10J.

    So work out the kinetic energy of the electron(½mv²) and put a minus sign in front. I get -8.93x10⁻¹⁹ J.


    but when i answer the question it says i am wrong? can someone please help me
     
  2. jcsd
  3. Jun 23, 2015 #2
    No need of minus sign dear.
    Minus sign represents the direction. But question don's ask a direction. So remove the minus sign. Then it'll be okay.:smile:
     
  4. Jun 23, 2015 #3

    Doc Al

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    Staff: Mentor

    Technically, you are correct: The work done must be negative. But apparently they just want the magnitude of the work, not the sign.
     
  5. Jun 23, 2015 #4


    it still says incorrect when i take out the negative which makes no sense bc i have no other way to get another answer.
     
  6. Jun 23, 2015 #5


    it still continues to say that it is incorrect, which makes no sense bc i know i did it correctly, i have no other way to get another answer. i don't know what is wrong with my answer.
     
  7. Jun 23, 2015 #6

    Doc Al

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    Staff: Mentor

    Do they specify the units they want you to use? (Joules makes sense, but there are other units.)
     
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