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

  • question_answer
    The diameter of the driving wheel of a bus is 140 cm. How many revolutions per minute must the wheel make in order to keep a speed of 66 km per hour?

    A)  200                

    B)  210                

    C)  250                

    D)  240 

    Correct Answer: C

    Solution :

    Radius of wheel = 70 cm \[\therefore \] Distance covered in 1 revolution             \[=2\times \frac{22}{7}\times 70=440\,cm\] Now, Speed \[=66\text{ }km/hr\] \[=\frac{66\times 1000\times 100}{60}cm/\min =110000\,cm/\min \] \[\therefore \]  Number of revolutions \[=\frac{110000}{440}=250\]


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