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4. The wheels of a car are of diameter 80 cm each. How many complete revolutions does each wheel make in 10 minutes when the car is travelling at a speed of 66 km per hour?

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Let the number of revolution of the wheel be n.

The circumference of the wheel is given by: 

        \\=\ 2\pi r\\\\=\ 2\pi \times 40\ =\ 80\pi\ cm

                                                                       

Now, the speed of the car is given by: 

         \\=\ 66\ Km/hr\ \\\\=\ 66\times \frac{100000}{60}\ cm/min\ \\\\=\ 110000\ cm/min.

Thus, the distance travelled in 10 minutes is:  =\ 1100000\ cm

According to the question, we get:

                                        n\times 80\pi\ =\ 1100000

or                                               n\ =\ 4375

Hence, the number of revolutions made by the wheel is 4372.

Posted by

Devendra Khairwa

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