RAJASTHAN PMT Rajasthan - PMT Solved Paper-2010

  • question_answer
               A rubber cord catapult has cross-sectional area \[25\,m{{m}^{2}}\] and initial length of rubber cord is 10 cm. It is stretched to 5 cm and then released to project a missile of mass 5 g. Taking \[{{Y}_{rubber}}\,=5\times {{10}^{8}}\,N/{{m}^{2}}\]. Velocity of projected missile is

    A)  \[20\,m/{{s}^{-1}}\]

    B)  \[100\,m/{{s}^{-1}}\]

    C)  \[250\,m/{{s}^{-1}}\]                    

    D)         \[200\,m/{{s}^{-1}}\]

    Correct Answer: C

    Solution :

    Potential energy stored in the rubber cord catapult will be converted into kinetic energy of mass \[\therefore \]  \[\frac{1}{2}m{{v}^{2}}=\frac{1}{2}\frac{\gamma A{{l}^{2}}}{L}\]                 \[v=\sqrt{\frac{\gamma A{{l}^{2}}}{mL}}\]                 \[=\sqrt{\frac{5\times {{10}^{8}}\times 25\times {{10}^{-6}}\times {{(5\times {{10}^{-2}})}^{2}}}{5\times {{10}^{-3}}\times 10\times {{10}^{-2}}}}\]                 \[=250\,\,m/s\]


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