# Homework Help: Motion in two dimensions

1. Apr 24, 2010

### mode656

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. Apr 25, 2010

### jdc15

When splitting the forces into components, you can't simply add the two together. You have to use the Pythagorean theorem.

3. Apr 25, 2010

### mode656

kk if i do that i end up with 289N which is still wrong
im not sure where i went wrong

4. Apr 25, 2010

### jdc15

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.

5. Apr 25, 2010

### mode656

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