NEET Physics NLM, Friction, Circular Motion NEET PYQ-NLM Friction Circular Motion

  • question_answer
    A nucleus of uranium decays at rest into nuclei of thorium and helium. Then,   [NEET 2015 (Re)]

    A) the helium nucleus has more kinetic energy than the thorium nucleus

    B) the helium nucleus has less momentum than the thorium nucleus

    C) the helium nucleus has more momentum than the thorium nucleus

    D) the helium nucleus has less kinetic energy than the thorium nucleus

    Correct Answer: A

    Solution :

    \[_{92}{{U}^{238}}{{\xrightarrow{\,}}_{92}}T{{h}^{238}}{{+}_{2}}H{{e}^{4}}\]
                According to law of conservation of linear momentum, we have.
                            \[\left| {{\mathbf{P}}_{\text{Th}}} \right|=\left| {{\mathbf{P}}_{\text{He}}} \right|=\mathbf{P}\]
                \[\Rightarrow \]   As, kinetic energy of an element,
                            \[KE=\frac{{{P}^{2}}}{2m}\]
                            where, m is mass of an element.        
                Thus,    \[KE\propto \frac{1}{M}\]
                So,      \[{{M}_{He}}<{{M}_{Th}}\Rightarrow {{K}_{He}}>{{K}_{Th}}\]


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