Question

The wheel of a motor cycle is of radius 21 cm. How many revolutions per minute must the wheel make so as to keep a speed of 77 km/h?

Answer 1

Distance travelled by wheel in one minute = $\frac{(77\times 100000)}{60}=\frac{770000}{6}cm/min$
Circumference of wheel =$\frac{2\times 22}{7}\times 21=132cm$
So required number of revolution in one minute = $\frac{\frac{(770000}{6})}{132}$
=972