# Find the magniture of the vector using the figure below

1. Jan 15, 2012

### Mdhiggenz

1. The problem statement, all variables and given/known data

Find the magnitude of the vector that is the sum of the three vectors , , and in the figure : figure is the link
http://imageshack.us/photo/my-images/14/yf0134.jpg/

2. Relevant equations

3. The attempt at a solution

What I did was obtain Ax=0 Bx=7.5

Ay=-8.00 and B13

My problem came when trying to get Cx and Cy.

The way the vector is placed in the figure confuses me but I got Cy= 12sin(25)= -10.87 since it is on the negative side, and Cx= 12Cos25=-5.07.

I then got the squareroot of Ax+Bx+Cx^2+Ay+By+Cy^2
Did I create the triangle wrong? If so how can I make sure to not make this same mistake

2. Jan 15, 2012

### Simon Bridge

That looks OK to me...
Haven't you got Cx and Cy the wrong way around though?
After all C is longer in x than it is in y and you have Cy as the bigger.

just a niggle, Cx is not 12Cos25
... you should have written Cx = -12Cos25 because that is what it is.
(you can lose marks that way)

You are used to the angle measured wrt the x axis ... in which case Cx=12Cos(205), which is the same.

3. Jan 15, 2012

### Mdhiggenz

Thank you!

4. Jan 15, 2012

### Simon Bridge

No worries - you see all the other angles were wrt the y axis? so that angle in C was 115 degrees anticlockwise from the y axis. Then you can use the same formula you used for the others.

You can always construct the kinds of angles that make the math easier for you.