A wheel of a car of radius 21 cm is rotating at 600 RPM. What is the speed of the car in km/hr?

Question: A wheel of a car of radius 21 cm is rotating at 600 RPM. What is the speed of the car in km/hr?

Solution:
The radius of the wheel measures 21 cm.

In one rotation, the wheel will cover a distance which is equal to the circumference of the wheel.
∴ in one rotation this wheel will cover 2 × π × 21 = 2 × (22/7) × 21 = 132 cm.

In a minute, the distance covered by the wheel = circumference of the wheel × rpm
∴ this wheel will cover a distance of 132 × 600 = 79200 cm in a minute.

In an hour, the wheel will cover a distance of 79200 × 60 = 4752000 cm.

Therefore, the speed of the car = 4752000 cm/hr = 47.52 km/hr