Speed of a Particle

1. Feb 12, 2009

julz3216

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

Consider the following position function.
r(t)= et(cos(t)i+sin(t)j+7tk)

Find the speed of a particle with the given position function.

2. Relevant equations

I know I take the derivative of the function but I cant seem to get speed.
I got v=e^t(cos(t)i+sin(t)j+7(t)k)+ e^t(-sin(t)i+cos(t)j+7k)

3. The attempt at a solution

I just cant find the speed, i think i may be just slightly off. I currently have speed is 7e^t(t+1) which is wrong.

2. Feb 12, 2009

rootX

Edit:

You are simply using "k" part, where is your i and j part. They don't cancel out.

Last edited: Feb 12, 2009