CET Karnataka Medical CET - Karnataka Medical Solved Paper-2012

  • question_answer
    Two bodies of masses m, and m^ are acted upon by a constant force F for a time t. They start from rest and acquire kinetic energies \[{{E}_{1}}\] and \[{{E}_{2}}\] respectively. Then \[\frac{{{E}_{1}}}{{{E}_{2}}}\] is

    A)  \[\frac{{{m}_{1}}}{{{m}_{2}}}\]              

    B)  \[\frac{{{m}_{2}}}{{{m}_{1}}}\]

    C)  \[1\]

    D)  \[\frac{\sqrt{{{m}_{1}}{{m}_{2}}}}{{{m}_{1}}+{{m}_{2}}}\]                  

    Correct Answer: B

    Solution :

    : The acceleration of the body of mass \[{{m}_{1}}\] acts upon by a constant F is           \[{{a}_{1}}=\frac{F}{{{m}_{1}}}\]                       ??.(i)            The acceleration of the body of mass \[{{m}_{2}}\] acts upon by a same constant F is \[{{a}_{2}}=\frac{F}{{{m}_{2}}}\] ???(ii) Starting from rest, the velocity acquired by mass  \[{{m}_{2}}\] in time t is \[{{\upsilon }_{1}}={{a}_{1}}t=\frac{F}{{{m}_{1}}}t\] (Using (i))        ??(iii) Starting from rest, the velocity acquired by mass \[{{m}_{2}}\] in the same time t is                     \[{{\upsilon }_{2}}={{a}_{2}}t=\frac{F}{{{m}_{2}}}t\](Using (ii))       ??.(iv)  Divide (iii) by (iv), we get \[\therefore \] \[\frac{{{\upsilon }_{1}}}{{{\upsilon }_{2}}}=\frac{{{m}_{2}}}{{{m}_{1}}}\]          ???.(v) Kinetic energy of mass \[{{m}_{1}}\] is              \[{{E}_{1}}=\frac{1}{2}{{m}_{1}}\upsilon _{1}^{2}\]           ???(vi) Kinetic energy of mass \[{{m}_{2}}\] is \[{{E}_{2}}=\frac{1}{2}{{n}_{2}}\upsilon _{2}^{2}\] ??.(vii) Divide (vi) by (vii), we get \[\frac{{{E}_{1}}}{{{E}_{2}}}=\frac{{{m}_{1}}}{{{m}_{2}}}{{\left( \frac{{{\upsilon }_{1}}}{{{\upsilon }_{2}}} \right)}^{2}}\] \[=\frac{{{m}_{1}}}{{{m}_{2}}}{{\left( \frac{{{m}_{2}}}{{{m}_{1}}} \right)}^{2}}\](Using (v)) \[=\frac{{{m}_{1}}}{{{m}_{2}}}\]


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