Find the average velocity over the time periods

[wind]

the displacement, in meters, of a ball rolling in a straight line on a grassy hill is given approximately by s= -t^2 + 6t + 5, where t is measured in seconds.

a)Find the average velocity over the time periods

te[2,4]

change in y divided by the change in x so..

v=f(x2)- f(x1) / x2 - x1
=45-21 / 4-2
=24 / 2
=12 m/s

but, the answer in the back of the book is 0m/s

Pleas help, thanks.

 

[skeeter]

s= -t^2 + 6t + 5

s(4) = -(4)² + 6(4) + 5 = -16 + 24 + 5 = 13

s(2) = -(2)² + 6(2) + 5 = -4 + 12 + 5 13

v_avg = [s(4) - s(2)]/(4 - 2) = (13 - 13)/2 = 0

 

[wind]

Thank you