Explain why
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The area through which water is flowing out of the hole in the vessel is small. According to equation of continuity ,

Area × velocity = constant

So the velocity of water flowing through the hole is large.

According to law of conservation of momentum,

m₁v₁ = m₂v₂

Due to this the vessel attains a backward velocity as there are no external forces acting on the system. So we can that water exerts a backward thrust on the vessel.