Curvilinear Motion: Rectangular Components

[aaronfue]

Homework Statement

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

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

Homework Equations

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

The Attempt at a Solution

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

r' = {3\pisin(\frac{\pi}{10}t) i + 3\picos(\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}

 

[ehild]

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

ehild