JEE Main & Advanced Physics Thermometry, Calorimetry & Thermal Expansion Question Bank Calorimetry

  • question_answer
    A bullet moving with a uniform velocity v, stops suddenly after hitting the target and the whole mass melts be m, specific heat S, initial temperature 25°C, melting point 475°C and the latent heat L. Then v is given by [NCERT 1972]

    A)            \[mL=mS\,(475-25)+\frac{1}{2}\cdot \frac{m{{v}^{2}}}{J}\]

    B)            \[mS(475-25)+mL=\frac{m{{v}^{2}}}{2J}\]

    C)            \[mS\,(475-25)+mL=\frac{m{{v}^{2}}}{J}\]

    D)            \[mS\,(475-25)-mL=\frac{m{{v}^{2}}}{2J}\]

    Correct Answer: B

    Solution :

                       Firstly the temperature of bullet rises up to melting point, then it melts. Hence according to \[W=JH\].                    Þ \[\frac{1}{2}m{{v}^{2}}=J.[m.c.\Delta \theta +mL]=J[m\,S\,(475-25)+mL]\]            Þ \[mS(475-25)+mL=\frac{m{{v}^{2}}}{2J}\]


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