Fri January 04, 2013 By: Shivasis Mohanty

You have a bag of cotton and an iron bar, each indicating a mass of 100 kg when measured on a weighing machine. In reality, one is heavier than other. Can you say which one is heavier and why?IN SOME BOOKS THE ANSWER IS THAT COTTON BAG IS HEAVIER AND IN OTHERS IT IS SAID THAT IRON BAR IS HEAVIER.PLEASE TELL ME WHICH ONE IS CORRECT.

Expert Reply
Sat January 05, 2013
The iron bar is heavier than the bag of cotton. This is because the surface area of thecotton bag is larger than the iron bar. Hence, more buoyant force acts on the bagthan that on an iron bar. This makes the cotton bag lighter than its actual value. Forthis reason, the iron bar and the bag of cotton show the same mass on the weighingmachine, but actually the mass of the iron bar is more that that of the cotton bag
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