Calculating Average Angular Velocity

[mathnoobie]

Homework Statement

At t=0 the current to a dc electric motor is reversed, resulting in an angular displacement of the motor shaft given by
theta(t)=246t-20.6t^2-1.47t^3

Calculate the average angular velocity for the time period from t=0 to the time calculated when the angular velocity of the motor shaft is 0.

Homework Equations

delta(omega)/delta(time)

The Attempt at a Solution

The time the velocity of the motor shaft is 4.14. I got that from taking the derivative and solving for t=0.
I'm confused as to why my answer is wrong, when I plug in 4.14 into
246-41.2t-4.41t^2 to calculate the average angular velocity I get.
(2(41.2)(4.14)-4.41(4.14)^2-246)/(4.14-0)
I get an answer of -59.46 rad/s.

Can't seem to find where I went wrong, I did this on paper as well as on calculator to make sure I wasn't punching it in wrong and I came out with approximately the same result.

 

[TSny]

Note that the question asks for average angular velocity (not instantaneous velocity).

 

[mathnoobie]

Note that the question asks for average angular velocity (not instantaneous velocity).

Ah... thank you, I was helping someone with this and just couldn't seem to find my error.