# Adding Vectors

http://img366.imageshack.us/img366/5171/phwq5.jpg [Broken]

Hello there. In lab, we measured vectors. I'm having a little concern on how to get X and Y. If I follow the books method, R_calc comes out too small compare to measure R. (Big % error).

X:
15.5+12.4cos37 = 25.4
Y:
0+9.3sin37 = 5.4
R:
square root of (25.4^2+5.4^2) = 26cm

If I do it my way, R is a lot closer to measure.

X:
15.3+12.4= 27.9cm
Y:
0 + 9.3 = 9.3 cm
R:
square root of (27.9^2+9.3^2) = 29.4 cm

The measurements (x1/2; y1/2; R m) are pretty accurate. What am I doing wrong? Thanks for any help.

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## Answers and Replies

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hage567
Homework Helper
OK, I will try to point out a couple of things:

http://img366.imageshack.us/img366/5171/phwq5.jpg [Broken]

Hello there. In lab, we measured vectors. I'm having a little concern on how to get X and Y. If I follow the books method, R_calc comes out too small compare to measure R. (Big % error).

X:
15.5+12.4cos37 = 25.4
I'm not sure I understand what you are attempting, but as I see it your x value is not correct. R is made up of x1 and b in this case. You need to find b, to solve it this way. So use trig to find b instead of x2. But it isn't a right triangle, so the resultant is a little more difficult to solve for.Y:
0+9.3sin37 = 5.4
R:
square root of (25.4^2+5.4^2) = 26cm

This is correct:If I do it my way, R is a lot closer to measure.

X:
15.3+12.4= 27.9cm
Y:
0 + 9.3 = 9.3 cm
R:
square root of (27.9^2+9.3^2) = 29.4 cm

The measurements (x1/2; y1/2; R m) are pretty accurate. What am I doing wrong? Thanks for any help.

Last edited by a moderator: