Although other important factors must be considered to determine the number of locomotive(s) required to pull a train up a hill, the power required just to "lift" the train in a gravitational field can be computed from: where power, mass, rate of elevation increase h h p mg p m t t   = = = =   . in north america, most railroad lines have a maximum grade of 1%: 1 ft of rise for every 100 ft of horizontal distance. therefore maximum rate of elevation of increase of the train, (h/t), is limited to about 1% of the train’s speed. a general electric et44c4 diesel-electric locomotive can produce about 4,400 hp to pull a train. if you assume that all of that power is available to "lift" the train, what is the maximum mass of the train, (in units of lbm), that one of these locomotives can pull up a 1% grade at a speed of 15 mph (22 ft/s)?