CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2003

  • question_answer
    An\[\alpha -\]particle of mass m suffers one dimensional elastic collision with a nucleus of unknown mass. After the collision the\[\alpha -\]particle is scattered directly backwards losing 75% of its kinetic energy. Then the mass of the nucleus is:

    A)  m                                          

    B)  2m                        

    C)  3m                        

    D)         1m

    E)  5m

    Correct Answer: C

    Solution :

    \[\frac{1}{2}{{m}_{1}}u_{1}^{2}-\frac{1}{2}{{m}_{1}}v_{1}^{2}=\frac{75}{100}\times \frac{1}{2}{{m}_{1}}u_{1}^{2}\] \[\Rightarrow \]               \[u_{1}^{2}-v_{1}^{2}=\frac{3}{4}u_{1}^{2}\] \[\Rightarrow \]               \[{{v}_{1}}=\frac{1}{2}{{u}_{1}}\]                              ?.. (1) Now      \[{{v}_{1}}=\frac{({{m}_{2}}-{{m}_{1}}){{u}_{1}}}{({{m}_{1}}+{{m}_{2}})}\] Thus,     \[\frac{1}{2}{{u}_{1}}=\frac{({{m}_{2}}-{{m}_{1}}){{u}_{1}}}{({{m}_{1}}+{{m}_{2}})}\] \[\Rightarrow \]               \[{{m}_{2}}=3{{m}_{1}}=3m\]


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