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.

Answer 1

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.