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A glass plate of length `10 cm`, breadth `1.54 cm` and thickness `0.20 cm` weigh `8.2 g` in air. It is held vertically with the long side horizontal and the lower half under water. Find the apparent weight of the plate. Surface tension of water `=7.3xx10^(-2)N//m` and `=9.8ms^(-12)` |
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Answer» Correct Answer - A Volume of the portion of the plate immersed in water is `10xx(1)/(2)(1.54)xx0.2=1.54cm^(3)` Therefore, if the density of water is taken as 1, Then uptrust =weight of the water displaced `=1.54xx1xx981509.2 dynes` Now, the total length of the plate in contact with the water surface is `2(10+0.2)=20.4 cm` `:.` Downward pull upon the plate due to surface tension `=20.4xx73=1489.2 dynes` `:.` Resultant upthrust `=1509.2-1489.2` `=20.0 dynes=(20)/(980)` `=0.0204 gm-wt` `:.` Apparent weight of the plate in water =weight of the plate in air-resultant uothrust `=8.2-0.0204=8.1796 gm`. |
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