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: Homework: Coulomb's Law

  1. Jan 14, 2014 #1
    1. The problem statement, all variables and given/known data
    A point charge q1 = -3.9 μC is located at the origin of a co-ordinate system. Another point charge q2 = 7.3 μC is located along the x-axis at a distance x2 = 7.8 cm from q1.
    1) What is F12,x, the value of the x-component of the force that q1 exerts on q2?

    2. Relevant equations

    3. The attempt at a solution
    [(-3.9*10^-6 C)*(7.8*10^-6 C)*(9*10^9 C)]/(0.078^2) m= -45 N

    but the answer is wrong I converted everything into metric units.

    Attached Files:

  2. jcsd
  3. Jan 14, 2014 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Converting to SI units can simplify things, but if you are frequently using different units it can work out better to convert the constants instead.


    I think you just had some rounding issues ... I'm getting a slightly different number off the same calculation.
  4. Jan 14, 2014 #3
    when I used your k value with no conversions I got -42.1 N. I guessed the program wanted a more accurate solution thanks.
  5. Jan 15, 2014 #4

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    When I used yours - I got 42.115N and mine got me 42.057N ...

    With conversion the calculation works out as:

    90*3.9*7.3/7.8^2 = 42.115
  6. Jan 15, 2014 #5
    must have been the order with my calculator . I have a ti-30x IIS which is harder to track parenthesis and slightly longer operations. thanks again
  7. Jan 17, 2014 #6


    User Avatar
    Homework Helper

    depends on whether q2 = 7.3 μC , or 7.8 μC .
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted