BHU PMT BHU PMT (Mains) Solved Paper-2009

  • question_answer
    The relative density of a material may be found by weighing it first in air and then in water. If its weight in air is (5.00 ± 0.05) N and weight in water is (4.00 ± 0.05) N. Then the relative density along with maximum permissible error will be quoted as

    A)  5.0 ± 11%           

    B)  5.0 ± 6%

    C)  5.0 ± 1%             

    D)  1.25 ± 5%

    Correct Answer: A

    Solution :

                     Let relative density be denoted by R, then                 \[R=\frac{{{w}_{air}}}{{{w}_{air}}-{{w}_{water}}}\]                 \[\Rightarrow \]               \[R=\frac{{{w}_{air}}}{w}=5\]                 Error in w is \[0.05+0.05\]                 \[\Rightarrow \]               \[\Delta w=0.10\,N\]                 \[\frac{\Delta R}{R}=\frac{\Delta {{w}_{air}}}{{{w}_{air}}}+\frac{\Delta w}{w}\]                 \[\Rightarrow \]\[\frac{\Delta R}{R}=\frac{0.05}{5}+\frac{0.1}{(5-4)}\]                 \[\Rightarrow \]\[\frac{\Delta R}{R}=0.01+0.1\]                 \[\Rightarrow \]\[\frac{\Delta R}{R}\times 100=11%\]                 So,      \[R=5\pm 11%\]


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