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Homework Help: Motion in 2d w/ constant acceleration

  1. Sep 16, 2007 #1
    1. The problem statement, all variables and given/known data

    In a tv set, an electron beam moves with horizontal velocity 2.7 x 10^7 m/s across the cathode ray tube and strikes the screen, 42 cm away. The acceleration of gravity is 9.8 m/s^2.

    How far does the electron beam fall while traversing this distance? Answer in units of m.

    2. Relevant equations


    [tex]v_{xo} = 2.7 x 10^7 m/s[/tex]
    [tex]\Delta{x} = .42 m[/tex]

    [tex]a_{y} = 9.8 m/s^2[/tex]
    [tex]\Delta{y} = ? m [/tex]

    [tex]a_{y} = 9.8[/tex]
    [tex]v= 9.8t + v_{y0}[/tex]
    [tex]y= 4.9t^2 + v_{y0}t + y_{0}[/tex]

    3. The attempt at a solution

    I first tried to solve for time:

    [tex].42 = 2.7*10^7(t)[/tex]
    [tex]t = 1.556*10^{-8}[/tex]

    Then, I tried solving for [tex]\Delta{y}[/tex]

    [tex]\Delta{y} = v_{0y}t + (1/2)gt^2[/tex]
    [tex]\Delta{y} = 0 + 4.9(1.556*10^{-8}[/tex]
    [tex]\Delta{y} = 1.186*10^{-15}[/tex]

    however, this is turning up as incorrect. Where did I go wrong? What am I doing incorrectly?
    Last edited: Sep 16, 2007
  2. jcsd
  3. Sep 16, 2007 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Looks OK to me. What makes you think it's wrong?

    (If it's an on-line system, be sure to use a reasonable number of significant figures.)
  4. Sep 16, 2007 #3
    It was indeed my significant figures!

    Thanks for taking a look at my work. :smile: I was afraid I was completely off.
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