How to determine Force from hor. position vector?

[ARJewell]

Homework Statement

An object with mass 5000 grams starts from rest and its motion is described by the horizontal position vector given. Determine the force acting on this object at the time t=9sec:

x(t)=(.01/3)t^4-(.08sqrt(t^5))

Homework Equations

F=ma

The Attempt at a Solution

Would I just take the second derivative of the equation and use 5000 as the mass in grams?

 

[aim1732]

Yes of course.