A cylinder containing water up to a height of 25 cm has a hole of cross-section 14cm2 in its bottom. It is counterpoised in a balance. What is the initial change in the balancing weight when water begins to flow out?

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 = AvInitial mass of water flowing out per second = AvdRate of change of momentum = Adv2Initial downward force on the flowing out water = Adv2So equal amount of reaction acts upwards on the cylinder.∴ Initial upward reaction = Adv2[As v = 2gh]∴Initial decrease in weight = Ad(2gh)= 2 Adgh = 2×(14)×1×980×25 = 12.5 gm-wt.