NEET Sample Paper NEET Sample Test Paper-27

  • question_answer If the length of second pendulum is decreased by 2% how many seconds it will lose per day?

    A) \[1927\text{ }sec.\]                 

    B) \[2727\text{ }sec.\]

    C) \[2427\text{ }sec.\]                 

    D) \[864\text{ }sec.\]

    Correct Answer: D

    Solution :

    We know that, the correct time period of the second pendulum in 2 seconds. Suppose I in the correct length). \[2=2\pi \,\sqrt{\frac{1}{g}}\]                        ?...(i) Given, Decrease in length \[=2%=\frac{2h}{100}l\] \[\therefore \] length after contraction \[=L=\frac{2l}{100}\] \[\Rightarrow \]            \[i=L\,\left( 1-\frac{2}{100} \right)\] New time period is given by \[t=2\pi \sqrt{\frac{l}{g}\left( 1-\frac{2}{100} \right)}\]            ??(ii) \[\left( \because \,\,\,t=2\pi \sqrt{\frac{l}{g}} \right)\] From equations (i) and (ii), we have, \[\frac{t}{2}=\sqrt{1-\frac{2}{100}}\]                     ??(iii) \[={{\left( 1-\frac{2}{100} \right)}^{1/2}}\] Using binomial theorem, we have \[t=2\left( 1-\frac{1}{2}\times \frac{2}{100} \right)\] \[\Rightarrow \] \[t=2\left( 2-\frac{2}{100} \right)\sec \] It is clear that it less than 2. \[\therefore \]  The clock gains time and time gained in 2 seconds, \[=\frac{2}{100}\,\,\sec .\] \[\therefore \] Total time gained per day be clock or time loss by day. \[=\frac{2}{100}\times \frac{24\times 60\times 60}{2}=864\sec .\]


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