Question

A glass plate of length `10 cm`, breadth `1.54 cm` and thickness `0.20 cm` weights `8.2 gm` in air, It is held vertically with the long side horizontal and the lower half under water. Find the apperent weight of the plate.
Surface tension of water `= 73 "dyne" per cm, g = 980 "cm"//"sec"^(2)`

Answer 1

The force acting on the plate are
`(i)` Buoyancive force of water acting upward
`B = rho_(1)V_(Sub) g = 1 xx (1.54 xx 10 xx 0.2)/(2) xx 980 = 1509.2 "dyne"`.
`(ii)` Weight of the system acting downward
`= (8.2) xx 980 "dyne"`
`(iii)` Force of surface tension acting downward
`= 2 (l xx b)T = 2(10 + 0.2) 73 = 1489.2`
So net downward force `= mg +` (surface tension force) `- B = (8.2) xx 980 + 1489.2 - 1509.2 = 8016.008 "dyne" = 8.1786 gm` force