question_answer

Water is flowing at a speed of 1.5 \[\text{m}{{\text{s}}^{\text{-1}}}\] through a horizontal tube of cross-sectional area \[\text{1}{{\text{0}}^{\text{-2}}}{{\text{m}}^{\text{2}}}\]and you are trying to stop the flow by your palm. Assuming that the water stops immediately after hitting the palm, the minimum force that you must exert should be (density of water \[\text{=1}{{\text{0}}^{3}}\text{kg}{{\text{m}}^{-3}}\])                               [JEE ONLINE 09-04-2014]

A)  15 N   

B)       22.5 N

C)  33.7 N

D)       45 N

Correct Answer: A

Solution :

[a] For 1 m length of horizontal tube

Mass of water M = density × volume

Therefore minimum force  (rate of change of momentum) = 10 × 1.5 = 15 N