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Chhattisgarh PMT Chhattisgarh PMT Solved Paper-2006

  • question_answer
    50.          A mass of 20 kg moving with a speed of 10 m/ s                 collides with another stationary mass of 5 kg. As a result of the collision both masses s; together.   The kinetic energy of the compos.  mass will be            

    A)  600 J                    

    B)  800 J

    C)  1000J                                   

    D)  1200J

    Correct Answer: B

    Solution :

    Given, \[{{m}_{1}}=20kg,{{u}_{1}}=10m/s,\] Using law of conservation of momentum,                 \[{{m}_{1}}{{u}_{1}}+{{m}_{2}}{{u}_{2}}=({{m}_{1}}+{{m}_{2}})v\]                 \[20\times 10+5\times 0=(20+5)\times v\] \[\therefore \]  \[v=\frac{200}{25}=8m/s\] Kinetic energy of the composite mass \[=\frac{1}{2}({{m}_{1}}+{{m}_{2}}){{v}^{2}}\] \[=\frac{1}{2}(20+5)\times {{(8)}^{2}}=25\times 32=800J\]


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