Question

Chapter 09, Problem 077 Your answer is partially correct. Try again. In the figure, two long barges are moving in the same direction in still water, one with a speed of 6.9 km/h and the other with a speed of 18 km/h. While they are passing each other, coal is shoveled from the slower to the faster one at a rate of 930 kg/ How much additional force must be provided by the driving engines of (a) the faster barge and (b) the slower barge if neither is to change speed? Assume that the shoveling is always perfectly min. sideways and that the frictional forces between the barges and the water do not depend on the mass of the barges.

Answer 1

force=rate of change of momentum=speed*rate of change of mass

here relative speed will be considered.

for the slower barge, relative speed=0

hence force required=0

for faster barge, reltive speed=18-6.9=11.1 km/hr=3.0833 m/s

rate of change of mass=930 kg/min=15.5 kg/seconds

then force required=15.5*3.0833=47.791 N

hence force required by faster barge=47.791 N

force required by smaller barge=0 N