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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)

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#### Solution

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.

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