Year 8 Interactive Maths - Second Edition

Practical Applications

A circle is symmetric about its centre and any one of its diameters.  Architects often use the circle's symmetrical properties when designing athletic tracks, recreational parks, buildings, roundabouts, Ferris-wheels, etc.  Artists and painters find the circle almost indispensable in their work.  Circular cylinders are used to print newspapers.  Engineers exploit the circle's symmetrical properties as seen by the use of the circle in making watches, clocks, bicycles, cars, trains, ships, aeroplanes, radios, telephones, trolleys, wheel-barrows, air-conditioners, rockets etc.  Civilisation has progressed dramatically because of the invention of the circular wheel.

Example 15

A bicycle wheel has a radius of 21 cm.

a.  Find the circumference of the wheel using π = 3.14; and calculate the distance covered by the bicycle in 1500 revolutions in kilometres.  Round your answer to 3 decimal places.

b.  In covering a distance of 3 km, how many revolutions does the wheel make to the nearest integer?

Solution:

a.

So, the circumference of the wheel is 131.88 cm.

So, the number of revolutions made is 2275.