# Curvilinear Motion: Rectangular Components

1. Jan 27, 2013

### aaronfue

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

What is the magnitude of the velocity at t=4.00s?

I would like to see if my approach and answer is correct.

2. Relevant equations

Position: r = {-30cos($\frac{\pi}{10}$t) i + 30sin($\frac{\pi}{10}$t) j - (7t) k} ft

3. The attempt at a solution

I took the first derivative to get the velocity and my equation came out to be:

r' = {3$\pi$sin($\frac{\pi}{10}$t) i + 3$\pi$cos($\frac{\pi}{10}$t) j - (7) k} $\frac{ft}{s}$

And after plugging in t=4, my velocity vector equation was: [(8.96)i + (2.91)j - (7)k] $\frac{ft}{s}$

Then my velocity magnitude was: 11.74 $\frac{ft}{s}$

2. Jan 27, 2013

### ehild

It is OK, but the result can not be accurate to four significant digits.

ehild