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A cart wheel makes 9 revolutions per second. If the diameter of the wheel is 42 cm, find its speed in km/hr.

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#### Solution

Circumference = 2 π r = π d

`= 22/7 xx 42`

= 132 cm = 1.32 m

Circumference= 1.32 m

No. of revolutions = 9 per second

No. of revolutions per hour = 9 x 60 x 60 = 32400

Distance covered in one hour= 32400 x 1.32 = 42768m/hour

Speed of the wheel in km/hour = `42768/1000 = 42.768` km/hour = 43 km / hr

Speed = 43 km/hr

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