1.

A piece of iron of density `7.8xx10^-3(kg)/(m^3)` and volume `100cm^3` is totally immersed in water. Calculate (a) the weight of the iron piece in air (b) the upthrust and (c ) apparent weight in water.

Answer» (a) Here, density of iron,`d=7.8xx10^-3(kg)/(m^3)`
volume of iron piece, `V=100cm^3=100xx10^-6m^3=10^-3m^3`
mass of iron piece, `M=Vxxd=(10^-4m^3)xx(7.8xx10^-3(kg)/(m^3))=0.78kg`
Weight of iron piece, `W=Mg=(0.78kg)(10(m)/(s^2))=7.8N`
(b) Upthrust, `F_B=` weight of water displaced
`=` volume of water displaced `xx` density of water `xxg`
`=`volume of iron piece `xx` density of water `xxg`
`=(10^-4m^3)(1000(kg)/(m^3))(10(m)/(s^2)=1N`
(c ) Apparent weight `=` true weight of iron piece`-`upthrust on iron piece in water
`=W-F_B=7.8N-1N`
`=6.8N`


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