RAJASTHAN PMT Rajasthan - PMT Solved Paper-2008

  • question_answer
    A spring of spring constant \[5\times {{10}^{3}}\,N/m\] is stretched initially by 5 cm from the unstretched position. Then the work required to stretch it further by another 5 cm is

    A)  12.50 N-m                         

    B)  18.75 N-m

    C)  25.00 N-m         

    D)         6.25 N-m

    Correct Answer: B

    Solution :

                    \[{{W}_{1}}=\frac{1}{2}k\times x_{1}^{2}\]                 \[=\frac{1}{2}\times 5\times {{10}^{3}}\times {{(5\times {{10}^{-2}})}^{2}}\]                 \[=6.25\,\,J\]                 \[{{W}_{2}}=\frac{1}{2}k{{({{x}_{1}}+{{x}_{2}})}^{2}}\]                 \[=\frac{1}{2}\times 5\times {{10}^{3}}{{(5\times {{10}^{2}}+5\times {{10}^{-2}})}^{2}}\]                 \[=25\,\,J\] Net work done\[={{W}_{2}}-{{W}_{1}}\]                 \[=25-6.25\]                 \[=18.75\,\,J=18.75\,\,N-m\]


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