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Question
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.
Solution
Diameter of the wheel = 60 cm
∴ Radius of the wheel = 30 cm
circumference of the wheel = 2πr
`=2xx22/7xx30`
`= 1320/7 "cm"`
Distance covered by the wheel in 1 revolution `= 1320/7 "cm"`
∴ Distance covered by the wheel in 140 revolutions`=(1320/7xx140xx1/100) "m"`
`=((1320xx140)/(7xx1000)xx1/100) "Km"= 264/1000 "Km"`
Now,
Distance covered by the wheel in 1 minute = Distance covered by the wheel in 140 revolutions `= 264/1000 "km"`
∴ Distance covered by the wheel in 1 hour `=264/1000xx60=15.84 "Km" //"h"`
Hence, the speed at which the boy is cycling is 15.84 km/h.
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