# Homework Help: (Simple) Vector Problemdon't see what I'm doing wrong

1. Sep 8, 2008

(Simple) Vector Problem..don't see what I'm doing wrong!!

1. The problem statement, all variables and given/known data

If the vector B is added to vector C = 3.7 i + 4.9 j , the result is a vector in the positive direction of the y axis, with a magnitude equal to that of C. What is the magnitude of B?

Here is what I did -

Magnitude is r = sq rt of Ax^2 + Ay^2 components

therefore, the magnitude of C is

3.7^2 + 4.9^2, take sq rt = 6.14 = magnitude of C

The question is for the magnitude of B. The resultant vector, according to the problem, has the same mag as C, so I would use the Pythagorean theorem =

A^2 + b^2 = C^2

6.14 ^2 + 6.14 ^2 = 75.3992, take sq rt = 8.68.

However this answer is not correct. I do not see where I went wrong, please help. Thank you!

2. Sep 8, 2008

### edziura

Re: (Simple) Vector Problem..don't see what I'm doing wrong!!

Your question is difficult to follow. From the statement of the problem, start by writing

Bx i + By j + Cx i + Cy j = sqrt[ (Cx)^2 + (Cy)^2 ] j

What's the next step?