posted by katie on .
A toy car has a mass of 120g, including two 1.5 V batteries connected in series. Suppose the motor that drives the car is 80\% efficient (i.e., 80\% of the electric energy goes to the drive wheels, 20\% is dissipated as heat) and that friction and air resistance are negligible. How much charge passes through the batteries during the time it takes the car to accelerate from rest to 1.5 m/s?
Change in kinetic energy of car = (1/2) m v^2
divide that by 0.8
The result is the energy taken from the battery, q V.
V is 1.5*2 = 3 volts
solve for q