# What does it mean vector in the positive dirction of the y-axis.

1. Oct 6, 2011

### tebes

1. The problem statement, all variables and given/known data
If vector a is added to vector b = 7.4i + 7.7j, the result is a vector in the positive direction of the y axis, with a magnitude equal to that of vector b. What is the magnitude of vector a?

2. Relevant equations

3. The attempt at a solution
(Is the vector in the positive direction of the y-axis same positive direction of x-axis?
cosθ=u.v/||u|| ||v||
||ab||=5=||b||.

Last edited: Oct 6, 2011
2. Oct 6, 2011

### Staff: Mentor

Positive direction of the y axis is: pointing straight up.

Positive direction of the x axis is: in a direction horizontally to the right.

This assumes the usual x-y orientation, with y axis vertical, and x axis horizontal.

3. Oct 6, 2011

### tebes

Does it mean the vector of a,b,and ab are pointing in the same direction? Therefore, the angle of the c is lying on x-axis or y=axis ? :)

4. Oct 6, 2011

### tebes

May I have some hints for this question ?
:)

5. Oct 6, 2011

### Staff: Mentor

No. (Mind you, I don't know what you mean by "the vector of a,b,and ab", but the answer is still no.)

In fact, I don't know what you mean by "b = 7.4 + 7.7" either. What do you think you mean?

6. Oct 6, 2011

### tebes

I'm sorry for my "hanging" sentences. ( b=7.4i + 7.7j ).

7. Oct 6, 2011

### tebes

The question is fixed. :)

8. Oct 6, 2011

9. Oct 6, 2011

### tebes

Unfortunately, no. I'm still thinking. I would be appreciate if you can help me out . :) thank you.

10. Oct 6, 2011

### SammyS

Staff Emeritus
A vector in "the positive direction of the y axis" will be in the form of pj, where p > 0 .

11. Oct 7, 2011

### Staff: Mentor

Draw a set of axes. Draw an arrow representing vector B. Now, add another vector to the end of B, of a magnitude & direction that makes the resultant sum to be a vector that points vertically upwards.