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Vectors: Finding Magnitude and Angle

  • Thread starter tensirk
  • Start date
  • #1
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Homework Statement



In the sum A+B = C, vector A has a magnitude of 10.0 m and is angled 46.5° counterclockwise from the +x direction, and vector C has a magnitude of 15.0 m and is angled 23.5° counterclockwise from the -x direction. What are the magnitude and the angle (relative to +x) of B?
________ m at _______ ° counterclockwise from the +x direction


Homework Equations


a2+b2=c2

The Attempt at a Solution


I have tried this:
A: (10cos(46.5))= 6.88; (10sin(46.25))= 7.25
C: (15cos(23.5))= 13.76; (15sin(23.5))= 5.98

Then:
13.76-6.88= 6.88
5.98-7.25=-1.27

After this I used the Pythagorean Theorem...

√(-1.27)2+(6.88)2 = 7m

However, this answer is incorrect.

From there I calculated tan-1(-1.27)/(6.88)= -10.46 degrees

Also obviously incorrect.

Help is greatly appreciated!
 

Answers and Replies

  • #2
gneill
Mentor
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2,773
Did you try sketching the vectors first?
 
  • #3
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Yes, but I am kind of unsure as to what "counterclockwise from the (-)(+)x direction" is referring to.
 

Attachments

  • #4
SteamKing
Staff Emeritus
Science Advisor
Homework Helper
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tensirk:

Your C vector is laid out incorrectly. Its angle is measured CCW from the negative x-axis
(remember, clockwise is always the same direction from the observer's viewpoint.)
 

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