JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2009

  • question_answer
        Two bodies of equal masses are connected by a light inextensible string passing over a smooth frictionless pulley. The amount of mass that should be transferred from one to another so that both the masses mole 50 m in 5 s is

    A)  30 %                                     

    B)  40 %

    C)  70%                                      

    D)  50%     

    Correct Answer: B

    Solution :

                    Since each mass is moving 50 m in 5 s, therefore using the relation \[s=ut+\frac{1}{2}a{{t}^{2}},\]we have \[50=0\times 5+\frac{1}{2}\times a\times {{5}^{2}}\] or            \[a=\frac{100}{25}=4\,m{{s}^{2}}\] Let mass of one become\[{{m}_{1}}\]and that of other \[{{m}_{2}},\]where\[{{m}_{1}}>{{m}_{2}}\]. As\[{{m}_{1}}\]moves downwards with acceleration                 \[a=4\,m{{s}^{-2}}\] \[\therefore \]  \[a=\left( \frac{{{m}_{1}}-{{m}_{2}}}{{{m}_{1}}+{{m}_{2}}} \right)g\] So,          \[4=\left( \frac{{{m}_{1}}-{{m}_{2}}}{{{m}_{1}}+{{m}_{2}}} \right)(10)\] \[\left( \frac{{{m}_{1}}-{{m}_{2}}}{{{m}_{1}}+{{m}_{2}}} \right)=\frac{4}{10}=\frac{2}{5}\] \[\therefore \]% of mass transferred                 \[=\left( \frac{{{m}_{1}}-{{m}_{2}}}{{{m}_{1}}+{{m}_{2}}} \right)\times 100\]                 \[=\frac{2}{5}\times 100\] \[=40%\]


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