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Homework Help: Speed of a proton?

  1. Sep 29, 2005 #1
    Speed of a proton???

    i just don't know where to start with this??? do i have to go back to basic physics??

    i tried using the charge of the single proton to find the force of the electric field, and then with that force find an acceleration maybe??? im way confused

    A uniform electric field has a magnitude of 2.8 103 N/C. In a vacuum, a proton begins with a speed of 2.1 104 m/s and moves in the direction of this field. Find the speed of the proton after it has moved a distance of 1.0 mm.

    your help would be greatly appreciated!
  2. jcsd
  3. Sep 29, 2005 #2


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    Science Advisor

    What you say sounds good to me! You know the strength of the field and you know the charge of the proton. Their product is the force on the proton and, since F= ma, that force divided by the mass of the proton is the acceleration. Now use d= (1/2)at2+ vt= 1 mm to determine the time it takes the proton to move 1 mm. Once you know that, the final speed is at+ 2.1 x104.
  4. Sep 29, 2005 #3
    hmmm i went through and did everything you said and i got 3.881 e10...... which seemed way off and it was...

    there was something i obviously did wrong, what was it?

    and thank you for your help
  5. Sep 29, 2005 #4


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    Staff: Mentor

    Maybe you put a decimal point in the wrong place in line 5? Maybe you multiplied instead of divided in line 7? It's kind of difficult for people here to tell you what you did wrong if you don't show us what you actually did, numbers and all.
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