Question

A boy is cycling such that the wheels of the cycle are making 140 revolutions per minute.if the diameter of the wheel is 60cm calculate the speed in km per hour in which the boy is cycling

Answer 1

Radius of the wheel = r = 60 / 2 = 30 cm

Circumference of the wheel = 2 Π r = (2 x 22 / 7 x 30) cm = 1320 / 7 cm

=> Distance covered by the wheel in 1 revolution = 1320 / 7 cm

=> Distance covered by the wheel in 140 revolutions = 1320 / 7 x 140 cm

= (1320 / 7 x 140 x 1 / 100000) km = 264 / 1000 km

This means that distance covered by the wheel in 1 minute = Distance covered in 140 revolutions

= 264 / 1000 km

Therefore, Distance covered in 1 hour = 264 / 1000 x 60 km = 15.84 km

Hence, the speed with which the boy is cycling is 15.84 km / hr

Answer 2

r = 30cm = 0.3m.

Circumference = 2πr = 2×22×0.3/7

Total revolution = 160
Distance = 160×2×22×0.3/7

Speed = distance / time
= 16×2×22×3/7×60 m/s

In km/h = 18/5 × 16×2×22×3/7×60
= 18.1028571429km/h