A 500-lb crate rests on a dolly as shown. The dolly has four 5-in.-diameter wheels with 0.5-in.-diameter axles. Knowing that the coefficients of friction are μs = 0.12 and μk = 0.08, determine the magnitude of the horizontal force P required
(a) For impending motion of the dolly,
(b) To keep the dolly moving at a constant speed. Neglect rolling resistance between the wheels and the floor.