In Fig. 9-72, two long barges are moving in the same direction instill water, one with a speed of 7.3 km/h and the other with aspeed of 17 km/h. While they are passing each other, coal isshoveled from the slower to the faster one at a rate of 960 kg/min.How much additional force must be provided by the driving enginesof (a) the faster barge and (b)the slower barge if neither is to change speed? Assume that theshoveling is always perfectly sideways and that the frictionalforces between the barges and the water do not depend on the massof the barges.
Explanation / Answer
F = dP / dt = v dm /dt here m ischanging and v remains constant F = (7.3 + 17) / 3.6 * 960 / 60 = 108N a) 108 N in the direction of thefaster barge b) -108 N in the direction of the slower barge