Question

A cart wheel makes 9 revolutions per second. If the diameter of the wheel is 42cm, find its speed in km per hour. (Answer correct to the nearest km)

Answer 1

The Circumference of a Circle with diameter d is πd
The Circumference of a Circle with diameter 42cm is π x 42

= `(22)/(7) xx 42`

= 22 x 6
= 132cm
⇒ distance moved in 1 revolution = 132cm
Total distance moved in 9 revolutions 
= 9 x 132cm
= 1188cm
Total distance moved in 1 second = 1188cm
⇒ Total distance moved in 1 hour 
= 1188cm x 60 x 60
= 4276800cm

= `(4276800)/(100 xx 1000)"km"`
⇒ Speed = 42.7km/hr.
∴ Speed = 42.7km/hr.