Explain why (a) To keep a piece of paper horizontal, you should blow over, not u

Question

Explain why

(a) To keep a piece of paper horizontal, you should blow over, not under, it

(b) When we try to close a water tap with our fingers, fast jets of water gush through the openings between our fingers

(c) The size of the needle of a syringe controls flow rate better than the thumb pressure exerted by a doctor while administering an injection

(d) A fluid flowing out of a small hole in a vessel results in a backward thrust on the vessel

(e) A spinning cricket ball in air does not follow a parabo

Explanation / Answer

a)As the air pressure above is greater than the air pressure below.

b)Fast jets of water gush as the diameter of pipe dereases as we close the pipe.

c)As the needle diameter is small the pressure of liquid is more when it comes out of the syringe.

d)The fluid flowing through a small hole gives a backward thrust given by

F = (dm/dt) x v

where (dm/dt) is mass flow rate and v is speed of fluid

e)A spinning cricket ball has difference in pressure between above and below points.Due to the pressure difference it does not follow a parabolic path.

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