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: Motion in two dimensions

  1. Apr 24, 2010 #1
    1. The problem statement, all variables and given/known data
    Three students push a box. Michael pushes with a force of 200 N at 0 degree. Shannon exerts a force of 150 N at 30 degrees, and Adam pushes with 175 N at 145 degrees. What is the magnitude of the net force?


    2. Relevant equations
    Some trig nothing special

    3. The attempt at a solution
    X Axis
    200+(cos30*150)=329.9N [E]
    cos45*175=123.7N [W]
    329.9-120=209.9N [E]
    Y Axis
    sin30*150=75N [N]
    sin45*175=123.7 [N]
    75+123.7=198.7 [N]

    209.9+198.7= 408.6N
    I am not sure if i did it right at all...i am self taught to any help is appreciated thanks in advance
     
  2. jcsd
  3. Apr 25, 2010 #2
    When splitting the forces into components, you can't simply add the two together. You have to use the Pythagorean theorem.
     
  4. Apr 25, 2010 #3
    kk if i do that i end up with 289N which is still wrong
    im not sure where i went wrong
     
  5. Apr 25, 2010 #4
    Well, at this part "329.9-120=209.9N [E]" I'm not quite sure where the 120 came from. You should be subtracting 175Ncos(180-145). As for the Y axis, at "sin45*175=123.7 [N]", you should be using 35 instead of 45.
     
  6. Apr 25, 2010 #5
    K i don't know why I'm having such difficulty with a question that seemed so easy at first =/
    Here is what i have after your suggestions

    X Axis
    200+(cos30*150)=329.9N (pretty sure you don't round until the end)
    cos35*175= 143N
    329.9-143=186.9
    Y Axis
    sin35*175=100N
    sin30(150)=75N
    100+75=175N
    Hit it with some Pythagorean
    and you get 256N

    Thank you for your help:)
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook