BHU PMT BHU PMT (Screening) Solved Paper-2007

  • question_answer
    When a long spring is stretched by 2 cm, its potential energy is U. If the spring is stretched by 10 cm, the potential energy in it will be

    A)  10 U                                     

    B)  25 U

    C)  U/5                                      

    D)  5U

    Correct Answer: B

    Solution :

                     Potential energy in a stretched spring is given by \[U=\frac{1}{2}k{{x}^{2}}\] \[\therefore \]  \[\frac{{{U}_{1}}}{{{U}_{2}}}={{\left( \frac{{{x}_{1}}}{{{x}_{2}}} \right)}^{2}}\]     Given, \[{{x}_{1}}=2cm=0.02m,{{x}_{2}}=10cm=0.1m\] Substituting the values, we have \[\frac{{{U}_{1}}}{{{U}_{2}}}={{\left( \frac{0.02}{0.1} \right)}^{2}}={{\left( \frac{1}{5} \right)}^{2}}=\frac{1}{25}\] \[\Rightarrow \]               \[{{U}_{2}}=25\,{{U}_{1}}=25\,U\]


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