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Homework Help: Just tell me what equations to use, or anything.

  1. Oct 4, 2009 #1
    1.An electron accelerates from rest through a potential difference of 206 V. What is its final speed? (in m/s)

    2. An electron that has a horizontal initial speed of 4.50 106 m/s enters a region that has an electric field of 120 V/m pointing vertically upward.
    (a)How long does the electron take to travel 9 cm in the horizontal direction?

    (b) In this same time, what is the vertical displacement of the electron? Treat up as positive.

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Oct 4, 2009 #2


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    Homework Helper

    Osulongboard, you should collect all the formulas for your class on a sheet of paper and write down what each one says. For example,

    F = qE says an electric field causes a force on a charge.
    a = F/m says a force causes a mass m to accelerate
    Energy = qV says a potential change gives a charge energy
    I = V/R says a potential causes a current in a resistor

    Once you have this list (and I've given you most of what you need for these questions), you must practise reading the problem and then finding the right equation in your list by looking at the words. In #1, you have "potential difference" in the question so you know you need a formula with a V in it, but which one? Well, the question tells you that the potential difference causes an electron to increase its speed - or energy. Look for the formula that says that.
  4. Oct 5, 2009 #3
    thanks a ton! got it figured out.
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