force acts on a 2.80-kg particle in such a way that the position of the
particle as a function of time is given by x = (3.0 m/s)t - (4.0
m/s2)t2 + (1.0 m/s3)t3.
(a) Find the work done by the force during the first 4.0 s.
(b) At what instantaneous rate is the force doing work on the particle at the instant t = 3.0 s?