Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Electric field / charged plates question.

  1. Sep 21, 2008 #1
    I have this as an online assignment and think I have the wrong answer, but the site is telling me the result is wrong and takes a percentage off my grade each time i send a wrong submission.

    I am just posting an image link because that way you guys can see the picture:

    http://img142.imageshack.us/my.php?image=screenhunter003xp5qz5.png

    Here is what I have so far:


    t = length of plates / horizontal velocity

    = 2.20 * 10-2 m / 18.0 m/s = 1.22 * 10-3 s

    In the same time, the drop must deflect by 'd' distance along vertical direction. By second equation of motion

    d = uy * t + (1/2) * ay * t2

    uy = initial velocity along vertical direction = 0

    ay = acceleration along vertical axis.

    => 0.300 * 10-3 = 0 * t + 0.5 * ay * (1.22 * 10-3)2

    ay = 3.0 * 10-4 / 1.49 * 10-6 = 2.01 * 102 m/s2

    __________________________________________________________

    F = q * E

    by Newton's second law F = m * a

    => m * ay = q * E

    q = m * ay / E = 1.0 * 10-11 * 2.01 * 102 / 7.90 * 104

    q = 2.54 * 10-14 C

    But this is wrong and the site won't give me a feedback. If anyone can help me out, I would be very thankful. : )
     
  2. jcsd
  3. Sep 21, 2008 #2

    Defennder

    User Avatar
    Homework Helper

    Check your value for ay again.
     
  4. Sep 21, 2008 #3
    I did, it is 2.01 *10^2. Sorry, when I pasted, all the carrot signs disappeared.

    Is there anything wrong with any of the steps?

    Thanks.
     
  5. Sep 21, 2008 #4
    anyone?
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook