The electric motor of a model train accelerates the train from rest to 0.660 m/s in 31.0 ms. The total mass of the train is 650 g. Find the average power delivered to the train during its acceleration.
a=(V-Vo)/t=(0.660-0)/0.031s=21.3m/s^2.
F = m*a = 0.650*21.3 = 13.85 N.
d = Vo*t + 0.5a*t^2.
d = 0 + 0.5*21.3*(0.031)^2 = 0.01023 m.
P = F*d/t = 13.85 * 0.01023 / 0.031=4.57
Joules/s = 4.57 Watts.