JCECE Engineering JCECE Engineering Solved Paper-2012

  • question_answer
    A body of density \[{{d}_{1}}\] is counterpoised by \[Mg\]of weights of density \[{{d}_{2}}\] in air of density\[d\]. Then, the true mass of the body is

    A) \[M\]                                   

    B) \[\frac{M(1-d/{{d}_{2}})}{(1-d/{{d}_{1}})}\]

    C)  \[M\left( 1-\frac{d}{{{d}_{2}}} \right)\]                

    D)  \[M\left( 1-\frac{d}{{{d}_{1}}} \right)\]

    Correct Answer: B

    Solution :

    Let \[{{M}_{0}}=\]mass of body in vacuum Apparent weight of body in air = Apparent weight of standard weights in air \[\Rightarrow \]Actual weight - up thrust due to displaced air = Actual weight - up thrust due to displaced air \[\Rightarrow \]               \[{{M}_{0}}g-\left( \frac{{{M}_{0}}}{{{d}_{1}}} \right)dg=Mg-\left( \frac{M}{{{d}_{2}}} \right)dg\] \[\Rightarrow \]               \[{{M}_{0}}=\frac{M\left( 1-\frac{d}{{{d}_{2}}} \right)}{\left( 1-\frac{d}{{{d}_{1}}} \right)}\]


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