A loaded railroad car has a mass of 30 Mg and is supported by eight 800-mm-diameter wheels with 125-mm-diameter axles. Knowing that the coefficients of friction are µs = 0.020 and µk =0.015, determine the horizontal force required
(a) to start the car moving,
(b) to keep the car moving at a constant speed. Neglect rolling resistance between the wheels and the track.