Two long barges are floating in the same direction in still water, one with a speed of 10 km/h and the other with a speed of 20 km/h. while they are passing each other, coal is shoveled from the slower to the faster one at a rate of 1200 kg/min; see fig. 7-35. how much additional force must be provided by the driving engines of each barge if neither is to change speed? assume that the shoveling is always perfectly sideways and that the frictional forces between the barges and the water do not depend on the weight of the barges.