# 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:**

In one revolution of the wheel the cycle covers a distance of circumference of the wheel i.e. 2πr, where r = radius of the wheel

__Circumference__ of the wheel = 2 × (22/7) × (60/2) = 1320/7 cm

In 140 revolutions of the wheel of the cycle the distance covered will be = 140 × 1320/7 m/hour = 20 × (1320) cm = 26400 cm = 264 m = 0.264km

Since this distance is covered in an hour the speed of the bicycle is 0.264 km/hour

**✦ Try This:** A boy is cycling such that the wheels of the cycle are making 126 revolutions per hour. If the diameter of the wheel is 90 cm, calculate the speed in km/h with which the boy is cycling.

In one revolution of the wheel the cycle covers a distance of circumference of the wheel i.e. 2πr, where r = radius of the wheel

Circumference of the wheel = 2 × (22/7) × (90/2) = 1980/7 m

In 126 revolutions of the wheel of the cycle the distance covered will be = 126 × 1980/7 m/hour = 18 × (1980) m/hour = 35640 m = 35.64km

Since this distance is covered in an hour the speed of the bicycle is 35.64 km/hour

**☛ Also Check: **NCERT Solutions for Class 8 Maths Chapter 11

**NCERT Exemplar Class 8 Maths Chapter 11 Problem 74**

## 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.

**Summary:**

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, the speed in km/h with which the boy is cycling is 0.264 km/hour

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