A boy is cycling in such a way that the wheels of his bicycle are making 140 revolutions per minute. If the diameter of a wheel is 60 cm, calculate the speed (in km/h) at which the boy is cycling.

Given diameter of wheel = d = 60 cm

Number of revolutions in one minute = 140

Number of revolutions in one hour = 140×60

Number of revolutions in one hour = 8400

Distance covered in one revolution = circumference of wheel

⇒ Distance covered in one revolution = πd

= 188.57 cm

Distance covered in one hour = Distance in 1 revolution × no. of revolutions

⇒ Total distance covered in one hour = 188.57× 8400

⇒ Total distance covered in one hour = 1583988 cm = 15.839 km

∴ speed with which boy is cycling = 15.839 km/hr

The speed with which boy is cycling is 15.839 km/hr

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