Problem 4 (25 pts) An 85-kg roller coaster cart is traveling 4 m/s at the top of a hill 50 meters off the ground. How fast is it traveling at the top of a second hill 20 meters off the ground? (a) Assume zero friction (15 pts). 50 m (b) Assume: non-zero friction with coefficient # = 0.1; the distance 20 m between the tops of the hills is 100 m; a centripetal acceleration during all the motion due to curvatures of the trajectory is negligibly small compared ............mmm to the acceleration of gravity g. (10 pts). 100 m