Explain why
(a). To keep a piece of paper horizontal, you should blow over, not under, it
(b). When w 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 parabolic trajectory.

Explanation

(a). When we blow over the piece of paper, the velocity f air increases. As a result, the pressure on it decreases in accordance with the bernoulli's theorem whereas the pressure below remains the same (atmospheric pressure). Thus, the ppaer remains horizontal.
(b). By doing so the area of outlet of water jet is reduced, so velocity of water increases according to equation of continuity av=constant.
(c). For a constant height, the bernoulli's theorem is expressed at `P+1//2rhov^(2)=`constant
In this equation, the pressre P occurs with a signel power whereas the velocity occurs with a square power. therefore, the velocity has more effect compared to the pressure. it is for this reason that needle of the syringe controls flow rate better than the thumb pressure exerted by the doctor.
(d). This is because of principle of conservation of momentum. while the flowing fluid carries forward momentum, the vessel gets a backward momentum .
(e). A spinning cricket ball would have followed a parabolic trajectory has there been no air. but because of air the magnus effect takes place. due to the magnust effect the spinning cricket ball deviates from its parabolic trajectory.