A glass plate of length 10 cm., breadth 1.5 cm. and thickness 0.2 cm., weighs 8.2 gm. In air. It is held vertically with long side horizontal and half the plate immersed in water. What will be its apperent weight ? Surface tension of water = 73 dynes//cm.

Answer

8.219 gm. Wt.

Explanation

Apparent weight, `W' =` weight of plate - upward thrust due to water+force due to surface tension `:. W' = mg - [l xx (b//2) xxd) rho_w g + S xx(l + d)2`
`= 8.2 xx 980 - [10 xx(1.5)/(2)xx0.2]xx1xx980`
` + 73 xx [10 + 0.2] xx 2 dyn e`
` = 8.2 - 1.5 + (73 xx 10.2 xx2)//980 gm. wt. = 8.219 gm wt`