A fat hose pipe is held horizontally by a fireman. It delivers water through a constricting nozzle at 1 litre/sec. If by increasing the pressure, the water is delivered at 2 litre/sec, the fireman now has to

If 'Q' be the discharge through the nozzle , then the force applied by water on the nozzle is given by F = p(1/a-1/A).Q2 . Where a = nozzle area , A = cross sectional area of hose and p = density of water . Therefore  F α Q2 . So when the discharge becomes two times , force on the nozzle becomes four times and this force acts in the forward direction . So the fireman has to push backward 4 times as hard