Haryana PMT Haryana PMT Solved Paper-2007

  • question_answer
    If \[{{K}_{s}},\]and \[{{K}_{p}},\] respectively are effective spring constants in series and parallel combination of springs as shown in figure, find \[\frac{{{K}_{s}}}{{{K}_{p}}}\]

    A) \[\frac{9}{2}\]                                   

    B) \[\frac{3}{7}\]

    C)  \[\frac{2}{9}\]                                  

    D)  \[\frac{7}{3}\]

    Correct Answer: C

    Solution :

                    In the arrangement shown in figure \[(I)\] the two springs are in series. The effective spring constant \[{{K}_{S}}\] of this arrangement is \[\frac{1}{{{k}_{s}}}=\frac{1}{k}+\frac{1}{2k}\]                 or            \[\frac{1}{{{k}_{s}}}=\frac{2+1}{2k}=\frac{3}{2k}\]                 \[\therefore \]  \[{{k}_{s}}=\frac{2k}{3}\] In the arrangement shown in figure (II) the two springs are in parallel. The effective spring constant \[{{k}_{p}}\] of this* arrangement is                 \[{{k}_{p}}={{k}_{1}}+{{k}_{2}}\]                 \[=k+2k=3k\] \[\therefore \]  \[\frac{{{k}_{s}}}{{{k}_{p}}}=\frac{2k/3}{3k}=\frac{2}{9}\]


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