Exercise 6.9
Why does a fireperson sometimes struggle when holding the pipe issuing water?
Not cross-checked
NCERT prints no numerical answer for this exercise, so this working has not been cross-checked against the book.
Because of Newton's third law — the pipe pushes the water forward, so the water pushes the pipe backward with an equal force.
The hose forces a large amount of water out of the nozzle at high velocity, i.e. it exerts a large forward force on the water.
Simultaneously the water exerts an equal and opposite force on the pipe, directed backwards.
This backward (recoil) force tends to push the pipe out of the fireperson's hands, so they must apply a large force to hold it steady — which is a struggle.
It is the same effect that drives the balloon in Activity $\displaystyle 6.7$ and lifts a rocket (Fig. $\displaystyle 6.30$).
