The radius of the wheel of a vehicle is 70 cm. The wheel makes 10 revolutions in 5 seconds. The speed of the vehicle is :

Distance covered in 5 sec :
$$\eqalign{ & = \left( {2 \times \frac{{22}}{7} \times 70 \times 10} \right)cm \cr & = 4400\,cm \cr & = 44\,m \cr} $$
Distance covered in 1 sec :
$$\eqalign{ & = \left( {\frac{{44}}{5}} \right)m \cr & = 8.8\,m \cr} $$
∴ Speed :
$$\eqalign{ & = 8.8\,m/\sec \cr & = \left( {8.8 \times \frac{{18}}{5}} \right)km/hr \cr & = 31.68\,km/hr \cr} $$