Question

what would be the apparent weight of an iron block of size 5x5x5cm when completely immersed in water•density of water is 7.8g/cc

Answer 1

Weight of iron block in air = density * volume        = 5 g/cm³ * 125 cm³  = 625 grams

As the density of iron is more than the density of water, it sinks or gets submerged totally in water.  We use the Archimedes law.
   Buoyancy force = weight of water displaced
                 = volume of iron block * density of water  
                 = 125 cm³ * 1 g/cm³ = 125 grams

Apparent weight = weight in air - buoyancy force
                 = 625 - 125 = 500 grams


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