The diameter of the driving wheel of a bus is 140 m. How many revolutions per minute must the wheel make in order to keep a speed of 66 km/h?

250

Diameter of the bus's wheel = 140 cm

Circumference of the wheel = 140Π cm = 140*22/7 = 440 cm = 4.4 m

Thus, 4.4m of the wheel = one revolution

Velocity to be achieved = 66 km/hr = 66000/60 = 1100 m/min

Velocity to be achieved in number of revolutions = 1100/4.4 = 250 revolutions/min

The correct answer is Option (3) → 250