# Thread: Vector problem. I am confused

1. ## Vector problem. I am confused

Can someone point out where I am going wrong?

The vector in the drawing has a magnitude of 750 units.

(a) Determine the magnitude of the x and y components of the vector , relative to the black axes.
Ax = 650 units
Ay = 375 units

(b) Determine the magnitude and direction of the x and y components of the vector , relative to the colored axes.
Ax' = 575 units
Ay' = 482 units

My question is why is Ay' not just 750cos50?

Thanks.

2. Two reasons: 1. You actually have a negative angle there. 2. It should be the sin function.

3. So if I plug that in I get -575. Is that correct?

4. So if I plug that in I get -575. Is that correct?
I don't think so. What expression are you evaluating?

5. 750sin50 and then making that negative. I don't really think that is correct though because that is just the negative of the x component and that doesn't make sense at all.

6. I think your confusing has to do with how to measure angles in polar coordinates. From where do you normally measure angles? And what's a positive angle? What's a negative angle?

7. You measure from what is usually the +x plane on a normal cartesian coordinate system. In this case it is the -y axis. A positive angle is measured in a counter-clock-wise direction and a negative angle is measured in a clock-wise direction

8. Right. So, relative to the red axes, what is the angle of A?

9. -40 degrees or 320 degrees.

10. Right. So what is your expression for x'? y'?