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 parabolic trajectory
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(a) according to Bernoulli theorem , for horizontal flow of fluid ,
P + 1/2dv² = constant
Therefore , when velocity of a fluid increases , it's pressure decreases and vice-versa.
When we blow over a piece of paper , the velocity of air above the paper increases . so, in accordance with Bernoulli theorem , the pressure of air decreases above the paper . due to the pressure difference of air between below and above the paper a lifting force act on paper and hence it remian horizontal.
(b) According to equation of continuity for steady flow of liquid the product of area of cross-section of the tube and velocity of liquid remains constant at each point . i.e.,
A1v1 = A2v2
Now, when we try to close a water tap with our fingers , the area of CSA of the outlet of water jet is reduced due to the restriction provided by the fingera and therefore , the velocity of water increases and fast jets of water gush through the openings between our fingers .
(c) according to Bernoulli's theorem,
P + 1/2 dv² = constant .so, the size of the needle controls the velocity of flow and the thumb pressure controls pressure. Therefore , size of the needle of a syringe controls flow rate better than thumb pressure.
(d) fluid flowing out of a small hole in a vessel have a large velocity and therefore a large momentum.As no external force is acting therefore according to law of conservation of momentum equal momentum in opposite direction and hence, a backward velocity is attained by the vessel. Therefore a backward thrust act on the vessel.
(e) a spinning cricket ball in air does not follow a parabolic trajectory due to magnus effect.
P + 1/2dv² = constant
Therefore , when velocity of a fluid increases , it's pressure decreases and vice-versa.
When we blow over a piece of paper , the velocity of air above the paper increases . so, in accordance with Bernoulli theorem , the pressure of air decreases above the paper . due to the pressure difference of air between below and above the paper a lifting force act on paper and hence it remian horizontal.
(b) According to equation of continuity for steady flow of liquid the product of area of cross-section of the tube and velocity of liquid remains constant at each point . i.e.,
A1v1 = A2v2
Now, when we try to close a water tap with our fingers , the area of CSA of the outlet of water jet is reduced due to the restriction provided by the fingera and therefore , the velocity of water increases and fast jets of water gush through the openings between our fingers .
(c) according to Bernoulli's theorem,
P + 1/2 dv² = constant .so, the size of the needle controls the velocity of flow and the thumb pressure controls pressure. Therefore , size of the needle of a syringe controls flow rate better than thumb pressure.
(d) fluid flowing out of a small hole in a vessel have a large velocity and therefore a large momentum.As no external force is acting therefore according to law of conservation of momentum equal momentum in opposite direction and hence, a backward velocity is attained by the vessel. Therefore a backward thrust act on the vessel.
(e) a spinning cricket ball in air does not follow a parabolic trajectory due to magnus effect.
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