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Homework Help: Please help With 2 Electric Questions Please

  1. Apr 17, 2005 #1
    Please help With 2 "Electric" Questions Please

    I don't want to bother you guys, but my little brother has an independent study unit due tomorrow and he can't seem to figure out these two questions. I'm not so great with physics since i'm taking biology related courses. Anyways the questions are as follows, i think they are actually very simple, but i just don't have the background to figure them out right now. So if anyone can post solutions to these, it'll help myself learn/understand it so i can relay it to my brother. thanks.

    1. An electron has a mass of 9.11 X 10^-31 kg. Originally, it's at rest. What speed will the electron have after it is accelerated through a potential difference of 5.67 X 10^3 V?

    2. A positively charged particle had a mass of 6.70 X 10^-27 kg. When it was accelerated through a potential difference of 4.50 X 10^3 V, it achieved a speed of 6.56 X 10^5 m/s. What charge did the particle have?

    Thanks again =).
  2. jcsd
  3. Apr 17, 2005 #2


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    They are energy problems. Potential difference and work are related through

    [tex]W = q \Delta V[/tex]

    And work is related to change of kinetic energy through

    [tex]W = \Delta K = \frac{1}{2}m(v_f^2-v_1^2)[/tex]
  4. Apr 17, 2005 #3
    hmm, interesting, based on the info that you have given, i've deduced that the answer to #1 can be obtained through:

    q/(4.555X10^-31) = vf^2

    where q is a charge in coulombs, and vf is the final velocity.

    how do i figure what q is?
  5. Apr 17, 2005 #4


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    [tex]\frac{2q\Delta V}{m} = v_f^2[/tex]

    I get q(1.2447 x 10^-28) = vf^2.

    The charge q is that of the electron. It is the elementary charge e = 1.602 x 10^-19 C.
  6. Apr 17, 2005 #5
    your info helped alot thanks.
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