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A cylinder containing water up to a height of `25cm` has a hole of cross-section `1/4 cm^(2)` in its bottom. It is counterpoised in a balance. What is the intial change in the balancing weight when water begin to flow up? A. increases of `12.5 gwt`B. increase of `6.25 gwt`C. Decrease of `12.5 gwt`D. Decrease of `6.25 gwt` |
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Answer» Correct Answer - C Let `A = the area of cross section of the hole `v` = Initial velocity of efflux `d`=density of water , Initial volume of water flowing out per second =`Av` Initial mass of water flowing out per second = `Avd` Rate of change of momentum = `Adv^(2)` Initial downward force on the flowing out water `=Adv^(2)` So equal amount of reaction actys upwards on the cylinder. `:. I nitial upward reaction = `Adv^(2) [As v = sqrt(2gh)]` `:. i nital decrease in weight = Ad(2gh)` `=2Adgh = 2 xx (1/4)xx1xx980xx25=12.5 gm-wt`. |
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