The subway train shown is traveling at a speed of 30 mi/hr in the west direction when the brakes are fully applied on the wheels of cars B and C, causing them to slide on the track, but are not applied on the wheels of car A. Knowing that the coefficient of kinetic friction is 0.35 between the wheels and the track, determine
a. the time required to bring the train to a stop
b. the force in each coupling
car a is 40 tons
car b is 50 tons
car c is 40 tons