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 acts upwards on the cylinder.

∴ ∴ Initial upward reaction = $\mathrm{Adv}^2$ [As $v = \sqrt{2gh}$ ]

Initial decrease in weight = Ad(2gh)

= 2Adgh $= 2 \times \left( \frac{1}{4} \right) \times 1 \times 980 \times 25 = 12.5$ gm-wt.