Mastering Physics Vector Question

In summary, the conversation is about a problem in mastering physics where the task is to express C in terms of vector A, vector B, and angle theta. The solution involves using the law of cosines and the feedback received was to check the signs. The correct solution is C = sqrt(A^2 + B^2 - 2ABcos(Pi-θ)). The conversation then moves on to the second part of the problem, which involves finding the angle phi between vector C and vector A. The attempted solution is arcsin(ABsin(pi - theta) / Csin(a)), but there is uncertainty about whether this is the correct approach.
  • #1
fishguts
9
0

Homework Statement



I am having a problem with a mastering physics problem. I am given this image
41119_b.jpg


I am to Express C in terms of vector A, vector B, and angle theta, using radian measure for known angles. I know theta is equal to pi - c.

Homework Equations



law of cosines
render?tex=C%5E2%3DA%5E2+%2B+B%5E2+-+2AB+%5Ccos%28c%29.gif



The Attempt at a Solution



By using the law of cosines the answer i got was

C = sqrt(A^2 + B^2 - 2ABcos(θ))

The feedback I got back from the program was to check my signs but everything apperas to be correct. Can someone help me out?
 
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  • #2
Hi,
Should'nt it be C = sqrt(A^2 + B^2 - 2ABcos(Pi-θ)) ?
As c is the angle opposite to C.
 
  • #3
muscaria said:
Hi,
Should'nt it be C = sqrt(A^2 + B^2 - 2ABcos(Pi-θ)) ?
As c is the angle opposite to C.

Thats right! I do not know how I missed that
 
  • #4
I am having trouble with the second part of the problem. I do not know if it is my input to the problem or if I have the problem totally wrong. I am told to:

Find the angle phi that the vector C_vec makes with vector A_vec.

I get arcsin(ABsin(pi - theta) / Csin(a))

For earlier solutions in the problem I found C = to pi - theta so U used that instad of c. Can anyone help me out?
 

FAQ: Mastering Physics Vector Question

1. What is a vector in physics?

A vector in physics is a quantity that has both magnitude and direction. It represents physical quantities such as displacement, velocity, and force.

2. How do you add or subtract vectors in physics?

To add or subtract vectors, you must first break them down into their components, which are the horizontal and vertical parts of the vector. Then, you can add or subtract the components separately to find the resultant vector.

3. What is the difference between a scalar and a vector?

A scalar is a quantity that has only magnitude, while a vector has both magnitude and direction. Examples of scalar quantities in physics include temperature and mass, while examples of vector quantities include velocity and acceleration.

4. How do you calculate the magnitude of a vector?

To calculate the magnitude of a vector, you can use the Pythagorean theorem, which states that the magnitude of a vector is equal to the square root of the sum of the squares of its components.

5. What is the importance of vectors in physics?

Vectors are important in physics because they allow us to accurately describe and analyze the motion of objects. They also play a crucial role in understanding forces and their effects on objects in motion.

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