10th Class Mathematics Areas Related to Circles Question Bank MCQs - Areas Related to Circles

  • question_answer
    If the area of a semi-circular field is \[\text{154}00\text{ sq m},\] then perimeter of the field is:

    A) \[160\sqrt{2}\,m\]

    B) \[260\sqrt{2}\,m\]

    C) \[360\sqrt{2}\,m\]

    D) \[460\sqrt{2}\,m\]

    Correct Answer: C

    Solution :

    [c] Let the radius of the field be r.
    Then,    \[\frac{\pi {{r}^{2}}}{2}=15400\]
                \[\frac{1}{2}\times \frac{22}{7}\times {{r}^{2}}=15400\]
                \[{{r}^{2}}=15400\times 2\times \frac{7}{22}=9800\]
                \[r=70\sqrt{2}\,m\]
    Thus, perimeter of the field
                \[=\pi r+2r\]
                \[=\frac{22}{7}\times 70\sqrt{2}+2\times 70\times \sqrt{2}\]
                \[=220\sqrt{2}+140\sqrt{2}\]
                \[=\sqrt{2}(220+140)=360\,\sqrt{2}m\]


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