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7th Class Mathematics Integers Question Bank Integers

  • question_answer
    Polymers are known to contract and expand with a decreases and increase in temperature (respectively). With every \[{{5}^{o}}C\] decrease in temperature, the length of a polymeric rod decreases by 8mm, and with every \[{{5}^{o}}C\] increase in temperature, its length increases by 10 mm. A rod was taken at room temperature. Its temperature was first lowered to \[{{20}^{o}}C\] below room temperature and its length was noted down. Its temperature was then increased to \[{{15}^{o}}C\] above room temperature and its length was again noted down. What was the difference between the lengths of the rod that were noted down at the beginning and end of the experiment?

    A)  17 mm                        

    B)  51 mm

    C)  52 mm     

    D)  2 mm

    Correct Answer: C

    Solution :

    (c) At beginning, let length \[=1:\text{ }20{}^\circ C\Rightarrow 4\]times \[5{}^\circ C:15{}^\circ C\Rightarrow 3\] times \[{{5}^{o}}C\] hence, difference in length \[=\left( 4\times 8 \right)+\left( 3\times 10 \right)\text{ }mm=52\,\,mm\]      


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