How Do I Correctly Calculate Vector C Using Unit Vectors?

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In summary, the conversation is about solving a physics problem involving vector addition and unit vectors. The problem includes finding the unit vector representation of Vector A and Vector B, expressing Vector C in terms of unit vectors, and finding the magnitude and direction of Vector C. The student is struggling with part B and has attempted it using trial and error, but their answer does not match the one in the solution manual. The error is likely due to an incorrect value for Vector B, which should be -1.2i - 2.1j when measured in standard counter-clockwise angles.
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J89
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Homework Statement



Here's the entire question. But I ONLY NEED help with part B. Part A and Part C I know how to do:

Vector A is 3.60 m with an angle of 70 degrees and Vector B is 2.4 m with an angle of 30 degrees downward.

a) Write Vector A and Vector B in terms of the unit i and j (already completed)

b) Use unit vectors express vector C where vector C = 3.00A-4.00B

c) Find the magnitude and direction of Vector C

Homework Equations


Vector addition..

The Attempt at a Solution



Here's the solution for part A.

Vector A= 3.60sin70=3.38
3.60cos70=1.23
so Vector A in terms of i and j= 1.23i + 3.38j

Vector B= 2.4sin30=1.2
2.4cos30=2.1
so vector B in terms of i and j= -1.2i + -2.1j (negative since going down)

For part b, I did trial and error, however when I looked at the answer in the back of the book, it was completely wrong. The answer is 12.01i + 14.94j and the numbers I got is much lower. I cannot do part C without getting part B first. Help!
 
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  • #2
It says C = 3A - 4B
Replace A with your answer (1.23i + 3.38j) and B with your (-1.2i - 2.1j).
Expand and simplify. The final answer should be a number times i plus a number times j.
 
  • #3
If angles are measured positive counter-clockwise from the positive x-axis (as standard) then your value for B is incorrect.
 
Last edited:

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