Well, if the position is x(t) = 2t² + 3t - 5
then the speed is x ' (t) = 4t + 3 (first derivative of 'x' wrt 't')
and the acceleration is x ' ' (t) = 4 (second derivative of 'x' wrt 't')
Apparently, then, the acceleration is constant, and is not a function of time.
After 2.7 seconds or 2.7 years, the acceleration is 4 .
Force = (mass) x (acceleration)
Force = (1.8) x (4)
Force = 7.2 newtons