A short train consists of a 400,000-lb locomotive and three 200,000-lb hopper cars. The locomotive exerts a

Question:

A short train consists of a 400,000-lb locomotive and three 200,000-lb hopper cars. The locomotive exerts a constant friction force of 40,000 lb on the rails as the train starts from rest.

(a) If there is 1 ft of slack in each of the three couplers before the train begins moving, estimate the speed v of the train just after car C begins to move. Slack removal is a plastic short-duration impact. Neglect all friction except that of the locomotive tractive force and neglect the tractive force during the short time duration of the impacts associated with the slack removal.

(b) If there is no slack in the train couplers, determine the speed v′ which is acquired when the train has moved 3 ft.