# Homework Help: 2D or 3D vector problem?

1. Sep 17, 2009

### elpermic

2D or 3D vector problem??

1. The problem statement, all variables and given/known data
Find the vector product of Vector A cross Vector B(expressed in unit vectors) of the two vectors. What is the magnitude of the vector product?

2. Relevant equations
Vector A= 5.00i + 2.00j
Vector B= 3.00i - 1.00j

3. The attempt at a solution

I know how to get the dot product of the two, but how do I find the cross product??

2. Sep 17, 2009

### CFDFEAGURU

Re: 2D or 3D vector problem??

This vector problem is 2D. You don't have a k component to represent the third dimension.

The cross product can be evaluated by

U x V = |U||V| * sin(angle between U and V)

|U| this means the "magnitude of U".

Hope that helps.

Thanks
Matt

3. Sep 17, 2009

### elpermic

Re: 2D or 3D vector problem??

The answer says -17.0k and 17.0. So shouldn't this mean it's a 3D problem? My teacher never taught me this in class and gave us 2 vector problems like this.

4. Sep 17, 2009

### CFDFEAGURU

Re: 2D or 3D vector problem??

No this is not a 3D problem. Where could the third dimension come from? The answers are equal and opposite in magnitude, that doesn't mean there is a third dimension.

What is your attempt at the solution? Can you find the magnitudes of the Vector A and Vector B?

Thanks
Matt

5. Sep 17, 2009

### elpermic

Re: 2D or 3D vector problem??

The magnitude of vector a is 5.38, vector b 3.16. I calculated the angle between the two to be 40.2 degrees. So I took ABsin(40.2) and got my answer is 11.0. The answer in the back says -17.0k, 17.0. I'm confused.. Is the book wrong or me?

6. Sep 17, 2009

### elpermic

Re: 2D or 3D vector problem??

Nevermind, I solved it.

7. Sep 17, 2009

### CFDFEAGURU

Re: 2D or 3D vector problem??

Good then, hope I helped you out.

Thanks
Matt