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Question
A boy is cycling such that the wheels of the cycle are making 140 revolutions per hour. If the diameter of the wheel is 60 cm, calculate the speed in km/h with which the boy is cycling.
Solution
The cycle makes 140 revolutions per hour.
Diameter of the wheel = 60 cm
Radius of the wheel = 30 cm
Circumference of a circle = 2πr
= `2 xx 22/7 xx 30`
= `(44 xx 30)/7`
= 188.57 cm
Distance cover in 140 revolutions
= 140 × 188.57
= 26400 cm
∴ Speed = `26400/100000` km/h ...[∵ 1 km = 100000 cm]
= 0.264 km/h
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