BCECE Medical BCECE Medical Solved Papers-2015

  • question_answer
    A ball of mass m moving at a speed v makes a head on collision with an identical ball at rest. The kinetic energy at the balls after the collision is 3/4th of the original. What is the coefficient of restitution?

    A)  \[1/\sqrt{3}\]               

    B)  \[1/\sqrt{2}\]

    C)  \[\sqrt{2}\]

    D)  \[\sqrt{3}\]

    Correct Answer: B

    Solution :

    Since, we know that in the case, when \[{{m}_{1}}={{m}_{2}}\] and \[{{v}_{1}}=0\] then,     \[v_{1}^{}=\left( \frac{1+e}{2} \right){{v}_{2}}\] and \[v_{2}^{}=\left( \frac{1-e}{2} \right){{v}_{2}}\] Given that, \[{{K}_{F}}=\frac{3}{4}{{K}_{i}}\]                 \[\Rightarrow \] \[\frac{1}{2}mv_{1}^{2}=\frac{1}{2}mv_{2}^{2}=\frac{3}{4}\,\,\left( \frac{1}{2}m{{v}^{2}} \right)\] Substituting the values, we get                 \[{{\left( \frac{1+e}{2} \right)}^{2}}+{{\left( \frac{1-e}{2} \right)}^{2}}=\frac{3}{4}\] \[\Rightarrow \] \[{{(1+e)}^{2}}+{{(1-e)}^{2}}=3\] \[\Rightarrow \]    \[2+2{{e}^{2}}=3\,\,\,\Rightarrow \,\,\,{{e}^{2}}=\frac{1}{2}\,\,\,\,\Rightarrow \,\,\,\,e=\frac{1}{\sqrt{2}}\]


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