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 60 cm then the speed per hour with which the boy is cycling is

• A. $12km/hr$
• B. $15.84km/hr$
• C. $13.75km/hr$
• D. $18km/hr$

Answer 1

The correct option is B $15.84km/hr$

$\therefore$ Diameter of the wheel $=60cm.$
$\therefore$ Radius of the wheel $=30cm$
$\therefore$ Circumference of the wheel $=2\pi r$
$=2\times \frac{22}{7}\times 30$
$=\frac{1300}{7}cm.$
$\therefore$ Distance covered in 1 revolution $=\frac{1300}{7}cm.$
$\therefore$ Distance covered in 140 revolutions
$=\frac{1300}{7}\times 140=1320\times 20$
$=26400cm=264m=0.264km.$
$\therefore$ Diastance covered by the wheel in 1 minute $=264km.$
$\therefore$ Distance covered by the wheel in 60 minute
$=0.264km\times 15.84km$
Hence, the speed with which the boy is cycling $=15.84km/hr$