# Mensuration-26

### From Homeworkwiki

**A boy is cycling such that the wheels of the cycle are making 140 revolutions per minute.**

**If the diameter of the wheel is 60 cm, calculate the speed per hour with which the boy is cycling.**

**Solution:** 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