Sandy is riding a bicycle with tires that have a diameter of 650 mm. A small twig, caught in the spokes, causes the tire to click once each revolution. Of Sandy hears 8 such clicks every 3 seconds then how fast is she cycling (to the nearest km/hr)

Explanation:

Sandy hears 8 such clicks every 3 seconds and a small twig, caught in the spokes, causes the tire to click once each revolution that means the wheel of the cycle is rotating at 8 rotations every 3 seconds or 8/3 rotation per second . In each rotation , it moves distance equal to its circumference .

circumference = 2π r = 2 x 3.14 x .65 / 2 m

= 2.041 m

In 8/3 rotation , distance covered = 8/3 x 2.041 = 5.44 m

So speed of cycle is 5.44 m per second

5.44 x 60 x 60 m per hour

19584 m per hour

= 19.584 km per hour .

= 20 km per hour approx.

one "light year" is the distance that light travels, through vacuum, in one julian year.   that's 365.25 days, of 24 hours each.