BCECE Engineering BCECE Engineering Solved Paper-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 \[\text{3}/\text{4th}\] 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, \[{{K}_{F}}=\frac{3}{4}{{K}_{1}}\] \[\Rightarrow \]               \[\frac{1}{2}mv_{1}^{'2}=\frac{1}{2}mv_{2}^{'2}=\frac{3}{4}\left( \frac{1}{2}m{{v}^{2}} \right)\] 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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