A luge and its rider, with a total mass of 81 kg, emerge from a downhill track onto a horizontal straight track with an initial speed of 30 m/s. If a force slows them to a stop at a constant rate of 3.9 m/s2, (a) what magnitude F is required for the force, (b) what distance d do they travel while slowing, and (c) what work W is done on them by the force? What are (d)F, (e)d, and (f)W if they, instead, slow at 7.8 m/s2?