A particle of mass `m` moves along a circle of radius `R` with a normal acceleration varying with time as `a_(n) = bt^(2)`, where `b` is a constant. Find the time dependence of the power developed by all the forces acting on the particle, and the mean value of this power averaged over the first `2` seconds after the beginning of motion, `(m = 1,v = 2,r = 1)`.