Adding 2 vectors. One is 20 degrees below x-axis

[dlouis]

I've done many other problems like this and understood them all but when it comes to 20 degrees below the x-axis it threw me off. I tried putting the angle to 340 degrees but that was incorrect. I know something has to be negative, i just can't keep guessing at getting it wrong. Hope someone can help!

Homework Statement

A vector A has a magnitude of 51.0 m and points in a direction 20.0° below the x axis. A second vector, B, has a magnitude of 70.0 m and points in a direction 43.0° above the x axis. Using the component method of vector addition, find the x- and y- components of the vector C.

Homework Equations

Vector A + Vector B = New Vector C

Cx = Ax + Bx
Cy = Ay + By

The Attempt at a Solution

I'm really not sure. In the book it says to put vector B at the head of vector A. I just drew each vector as a separate triangle and solved for Ax, Ay and so on. Like i said before, i just need to know what to do with the "20 degrees below the X-axis. Is it -20? 340? I've tried both and they came out wrong so help! Thanks again.

 

[edziura]

"I'm really not sure. In the book it says to put vector B at the head of vector A."

This is one way of finding C, but is not the method you are asked to use

"I just drew each vector as a separate triangle and solved for Ax, Ay and so on."

This sounds like what they are asking you to do.



"Like i said before, i just need to know what to do with the "20 degrees below the X-axis. Is it -20? 340? I've tried both and they came out wrong so help! Thanks again."

You should be able to use either -20 deg or +340 deg. Make sure your calculator is i degree mode, if that's how you chose to do the calculation.

In any case

Ax = 51 cos(-20) = 51 cos(340) = 49.9

Ay = 51 sin(-20) = 51 sin(340) = -17.4

 

[dlouis]

Thanks a lot for the help! This is a great forum. I'm glad I found it.