## Book: RS Aggarwal - Mathematics

### Chapter: 18. Area of Circle, Sector and Segment

#### Subject: Maths - Class 10th

##### Q. No. 34 of Exercise 18B

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34
##### The diameter of the wheels of a bus is 140 cm. How many revolutions per minute do the wheels make when the bus is moving at a speed of 72.6 km per hour?

Given diameter of wheel of bus = d = 140 cm

Speed of bus = 72.6 km/hr

Distance covered by bus in one hour = 72.6 km = 7260000 cm

Distance covered in one minute = 121000 cm eqn1

Let the number of revolutions made by wheel per minute = x

Distance covered by wheel in one revolution = circumference of wheel = 2πR

Distance covered by wheel in one revolution = 2π(70)

(putting value of R)

= 2×22×10 = 440 cm

Total distance = No. of revolution× Distance covered in1 revolution

On putting the required values we get,

121000 = 440×(x)

x = 275

Number of revolutions made per minute is 275.

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