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 paper, the velocity of air blow increases and hence pressure of air on it decreases (ac cording to Bernoulli's theorem), where as pressure of air below the paper is atmospheric. hence, the paper stays horizontal .
(b) By doing so the area of outlet of water jet is reduced, so velocity of water increases ac cording to equation of continuity. `a upsilon = a consta nt`
(c ) When a fluid is flowing out of a small hole in a vessel, it acquires a large velocity and hence possesses large momentum. since no external force is acting on the system, a backward velocity must be attained by the vessel (ac cording to law of conservation of momentum). As a result of it, an impulse (backward thrust) is experienced by the vessel.
(d) Here, size of the needle controls velocity of flow and thumb pressure controls pressure. Ac cording to Bernoulli's theoram , `P = rho gh + 1/2 rho upsilon^(2)` = a constant shows that P oc curs with power one and `upsilon` oc cours with power two, hence the velocity has more influence. that is why the needle has a better control over flow.
(e ) N/A.