11th Class Physics Work, Energy, Power & Collision / कार्य, ऊर्जा और शक्ति Question Bank 11th CBSE Physics Work, Energy, Power & Collision

  • question_answer
    A spring of force constant k is cut into two pieces of lengths \[{{l}_{1}}\] and \[{{l}_{2}}\]. Calculate force constant of each part.

    Answer:

                    For a spring \[\text{k}\propto \frac{1}{l}\].     \[\therefore \]\[{{\text{k}}_{\text{1}}}\propto \frac{1}{{{l}_{1}}}\], \[{{\text{k}}_{\text{2}}}\propto \frac{1}{{{l}_{2}}}\]  and \[\text{k}\propto \frac{1}{{{l}_{1}}+{{l}_{2}}}\] \[\therefore \]\[\frac{{{k}_{1}}}{k}=\frac{{{l}_{1}}+{{l}_{2}}}{{{l}_{1}}}=1+\frac{{{l}_{2}}}{{{l}_{2}}}\]                                or            \[{{\text{k}}_{\text{1}}}=\text{ k}\left( 1+\frac{{{l}_{2}}}{{{l}_{1}}} \right)\] and \[\frac{{{k}_{2}}}{k}=\frac{{{l}_{1}}+{{l}_{2}}}{{{l}_{2}}}=\frac{{{l}_{1}}}{{{l}_{2}}}+1\]              or                \[{{\text{k}}_{2}}=\text{ k}\left( 1+\frac{{{l}_{1}}}{{{l}_{2}}} \right)\] Note : If \[{{\text{l}}_{\text{1}}}={{\text{l}}_{\text{2}}},\text{ }{{\text{k}}_{\text{1}}}=\text{ }{{\text{k}}_{\text{2}}}=\text{2}k\] i.e. when length is halved, spring constant of each half becomes twice.  If \[\frac{{{l}_{1}}}{{{l}_{2}}}=\frac{1}{n}\], then \[{{\text{k}}_{\text{1}}}=\text{ k}\left( \text{l }+\text{ n} \right);{{\text{k}}_{\text{2}}}=\text{ k}\left( 1+\frac{1}{n} \right)\]


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