Calculating Average Velocity of Dropped Bolt From High-Rise Building

[Draggu]

Homework Statement

A construction worker drops a bolt while working on a high-rise building 320m above the ground. After t seconds, the bolt has fallen a distance of s metres, where s(t) = 320-5t^2, 0 <= t <=8

Find the average velocity for the interval 3<=y<=8

Homework Equations

The Attempt at a Solution

I used the formulas $$\Delta$$s / $$\Delta$$t
which then =
s(8) - s(3) / (8-3)

~
~
=55

Is this right?

 

[snipez90]

The magnitude is correct but I think you want to keep the negative sign to indicate direction.