JEE Main & Advanced Physics Nuclear Physics And Radioactivity Question Bank Mock Test - Modern Physics

  • question_answer
    A nucleus of mass number A, originally at rest, emits an a-particle with speed v. The daughter nucleus recoils with a speed

    A) \[\frac{4v}{A-4}\]         

    B) \[\frac{4v}{A+4}\]

    C) \[\frac{2v}{A+4}\]        

    D) \[\frac{2v}{A-4}\]

    Correct Answer: A

    Solution :

    [a] The emission of an \[\alpha \]-particle from the atom of element reduces its atomic number by 2 and mass number by 4. Hence, the radioactive emission is as follows; \[_{Z}{{X}^{A}}{{\xrightarrow{\alpha -particle}}_{Z-2}}{{Y}^{A-4}}+{}_{Z}H{{e}^{4}}(\alpha \text{-}particle)\]Also from law of conservation of momentum, \[m\times 0={{m}_{y}}{{v}_{y}}+{{m}_{\alpha }}{{v}_{\alpha }}\] \[=(A-4){{v}_{y}}+4v\] \[\Rightarrow {{v}_{y}}=\frac{4v}{A-4}\]


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