Position of toy moving on straight track

[dvdqnoc]

Homework Statement

The position of a toy locomotive moving on a
straight track along the x-ais is given by the
equation

x = t^6 - 6t^2 + 9t

where x is in meters and t is in seconds.

The net force on the locomotive is equal to
zero when t is equal to _______?

Answer in units of s.

Homework Equations

x = t^6 - 6t^2 + 9t
http://www.glenbrook.k12.il.us/gbssci/phys/Class/1DKin/U1L6a1.gif

The Attempt at a Solution

I tried to get the acceleration equation by taking the second derivative of the position equation, setting it to zero, and solving for t... but doesn't look right.

 

[learningphysics]

The procedure you described should give you the answer... where did you get stuck?