Question

A bicycle wheel, diameter 56 cm, is making 45 revolutions in every 10 seconds. At what speed, in kilometer per hour. Is the bicycle travelling?

Answer 1

ok, here's what we got.
radius=diameter/2=56/2=28cm

now, we are gonna find Periphery
Periphery=2πr
=(2)*(3.14)*(28)
=176 cms per rotation 

so now it goes for 176 cms per rotation. and we are told about 45, so
according to the speed-distance/time, we must find the distance first.

Now it goes on 45 revolutions per 10 seconds that means it goes on 45*6 revolutions per 10*6 seconds, that means 270 revolutions per minute. and similarly to find the hour rate it goes on 270*60 rotation per hour [1 min*60]

that means it's going on 16200 revolutions per hour. Now multiply the 16200 with the Periphery.

=16200*176
=2851200 centimeters per hour. 

Now convert the centimeters into kilometers, that means the answer is.... 28.512 kilometers per hour.
so your answer is 28.512 Km/h.

By the way, nice question. ^_^

Answer 2

$28.512 \frac{km}{hr}$