# Homework Help: Three Vectors - Resultant vector magnitude?

1. Sep 4, 2011

### KendrickLamar

1. The problem statement, all variables and given/known data
Three vectors are shown in the figure (A = 68.0 ; qB = 54.0°). Their magnitudes are given in arbitrary units. What is the magnitude of the resultant vector?

2. Relevant equations
here's the image that goes with it

3. The attempt at a solution
well i figure the angle would be 98 then i guess im just looking for the missing side which is the resultant vector but i tried some trig functions and failed, not really sure what to do, this is pretty basic but i haven't looked at any physics in about 3-4 years.

thanks if u can help

2. Sep 4, 2011

### rock.freak667

The easiest way would be to split B and A into both vertical and horizontal components. Then find the sum of the vertical (y) and sum of the horizontal (x) then apply

$$R=\sqrt{x^2+y^2}$$

Do you know remember how to split a vector into components?

3. Sep 4, 2011

### KendrickLamar

haha not really i feel kinda dumb now, can u quickly remind me? but even if u split it, and you're trying to get that other side, can't u NOT use the pythagorean theorem since theres no right angle

Last edited: Sep 4, 2011
4. Sep 4, 2011

### rock.freak667

How to split them: http://www.grc.nasa.gov/WWW/k-12/airplane/vectpart.html" [Broken]

You would be splitting them into horizontal and vertical vectors so the right angle is always there.

Once you split all into horizontal and vertical, you can sum the individual verticals to get the resultant vertical (y) and similarly sum the horizontals to get the resultant horizontal (x). Then apply the formula.

Last edited by a moderator: May 5, 2017
5. Sep 4, 2011

### KendrickLamar

what i dont get is, after u split it what are u exactly looking for because then you're just solving for A and B which are already given to you? A= 68 B =40 so wouldn't the purpose of splitting it into components be to get those values, however they're already provided.

6. Sep 4, 2011

### rock.freak667

You are give A and B at the particular angles, if you split into the components then you get the resultants in the x and y directions, which is what you want.