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: Electric Charge and Force

  1. Aug 29, 2016 #1
    1. The problem statement, all variables and given/known data
    Two identical balls (B and C) with a mass of .5 g are suspended from two strings as shown above. The balls carry equal charges +10nC each and are separated by a distance of 4 cm.
    A. Draw the free-body diagram and show all forces applied to ball C.
    B. Find the tension force in the string BC.
    C. Draw free-body diagram and show all forces applied on ball B
    D. Find the tension force in string AB
    E. Answer question a, b, c, d for the situation when the balls have equal but opposite charges (charge on B is positive and charge on C is negative).

    Ball C mass= 0.5g=0.0005Kg

    2. Relevant equations

    3. The attempt at a solution
    Okay so i thought the regular force tension equation would work but it didnt. I used Ft=w+ma. Using the variables I put the variables in each one. I did Ft=0.0005kg*9.81m/s^2+0.0005kg*0m/s^2 and got 0.004905, but turns out that is not the correct answer. The answer I'm supposed to get is 0.00546 N and I don't know what to do. Also I'm not sure what would work.

    My free body diagram, the first one is for Part A and the second one is for Part C.
    View attachment 105387 View attachment 105388
    https://www.physicsforums.com/attachments/free-body-diagram-one-png.105387/ [Broken]https://www.physicsforums.com/attachments/free-body-diagram-two-png.105388/ [Broken]
    [Moderator's edit note: Images retrieved from member's repeat post of this problem]
    Last edited by a moderator: May 8, 2017
  2. jcsd
  3. Aug 29, 2016 #2
    Can you draw the free-body diagram?
  4. Aug 29, 2016 #3
    Yes I already drew it.
  5. Aug 29, 2016 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    We can't see it .
  6. Aug 29, 2016 #5
    Don't mind the things above my drawing

    Attached Files:

  7. Aug 29, 2016 #6


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    @berkeman has already told you that it's nearly impossible to see content of your posted images. This one is no better.

    Also, it's quite confusing when you use the same title on more than one thread.
  8. Aug 29, 2016 #7
    I'm sorry. I'm just new to this website and I'm looking for help. But, what's a better way of showing my free body diagram?
  9. Aug 29, 2016 #8


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Take better pictures. Use some image enhancement app.

    Learn to type equation and math symbols directly to this site.
  10. Aug 29, 2016 #9


    User Avatar

    Staff: Mentor

    Hi Cglez1280,

    You might try a drawing program such as MS Paint or Visio or something similar to produce basic diagrams. That or find a way to make your camera images more clear; Lighting and focus can be problematical for phone cameras and they are not often very good for close-ups of handwriting.

    Personally I use Visio to create most diagrams that I need to post. Occasionally I'll capture an image by downloading and saving it, or 'cutting' it with a screen "snipping tool", and then I'll use use Visio or Paint to modify it.

    Whatever you choose it's in your best interest to make it as easy as possible for helpers to read your content; Volunteers are under no obligation to spend time deciphering offerings, and they may well just move on to a thread which is easier to deal with.
  11. Aug 29, 2016 #10
    You may find it easier if the free-body diagram shows both balls (ball B and ball C). Each ball will have three forces acting on it. Also, be sure to label and dimension the strings.

    Note that this is a static analysis -- nothing is moving.
  12. Sep 2, 2016 #11


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    The problem is the fbd doesn't appear to show all the forces acting on the balls. One force has been missed despite the title of this thread.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted