9th Class Mathematics Surface Areas and Volumes Question Bank Surface Areas and Volumes

  • question_answer
    The volume of a cylinder of radius r is 1/4 of the volume of a rectangular box with a square base of side length x. If the cylinder and the box have equal heights, what is the value of r in terms of\[x\]?

    A) \[\frac{{{x}^{2}}}{2\pi }\]                              

    B) \[\frac{x}{2\sqrt{\pi }}\]

    C)         \[\frac{\sqrt{2x}}{\pi }\]

    D)        \[\frac{x}{2\sqrt{\pi }}\]                        

    Correct Answer: B

    Solution :

    Let the height of cylinder and rectangular box be h. Volume of cylinder\[=\pi {{r}^{2}}h\] \[\therefore \]Volume of rectangular box\[=x\times x\times h={{x}^{2}}h\] According to question, Volume of cylinder \[=\frac{1}{4}\times \]Volume of rectangular   box \[\Rightarrow \]\[\pi {{r}^{2}}h=\frac{1}{4}\times {{x}^{2}}h\Rightarrow {{r}^{2}}=\frac{{{x}^{2}}}{4\pi }\]or \[r=\frac{x}{2\sqrt{\pi }}\]


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