1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
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: Coulombs Law with vectors question help, test tomorrow.

  1. Oct 3, 2012 #1
    1. The problem statement, all variables and given/known data[/b]

    1. Charge A (-2uC) is 0.10m left of charge B (+3uC), with charge C (+4uC), 0.075m below charge B, forming a right angle triangle with the right angle at B. Find the net electrostatic charge on C

    if its confusing the 0.10 is the opposite of the hypotenuse with the 0.075m being the adjacent.

    i dont how to draw a damn triangle i cant do it with just normal symbols but if oyu dont understand the triangle i will try to explain it further
    2. Relevant equations

    3. The attempt at a solution
    Fe(b on c) = (8.99*10^9)(3*10^-6)(4*10^-6)/ .075^2 = 19.17866666..

    Fe (a on c) = first i found the hypotenuse, (.1^2+.075^2) = .015625m

    then found Fe, K * ( 4*10^-6) (2*10^-6)/.015625^2 = 294.58432

    I found the angle at C, by using pythagoras, tan-1(0.10/.075) = 53.13010235, then found the angle to use to find the x and y component of Fe (a on c) by subtracintg 53.. from 90, which is 36.86089765..

    Fe (aonc x) = 294... * cos36... = 235.667456
    Fe (aonc y) = 294... * sin 36... = 176.750592

    then [itex]\sqrt{235..^2 + 176...^2}[/itex] which equals back to 294.58432.

    I may have done the whole Fe ( a on c) wrong, if i did i dont know where.

    The answer is 16.8N 12.6 degrees W of S
    Last edited: Oct 3, 2012
  2. jcsd
  3. Oct 4, 2012 #2


    User Avatar
    Homework Helper

    You made a mistake when calculating the hypotenuse: .015625 is the square of of the hypotenuse, you do not need to square again in the equation for the force. .

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook