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The wheel of the car makes 10 revolutions per second. If its diameter is 70 cm, find the speed of the car in km per hour.

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#### Solution

Circumference = 2 π r = π d

`= 22/7 xx 70 = 220 "cm" = 2.2 "m"`

Circumference = 2.2 m

No. of revolutions = 10 per second

No. of revolutions per hour = 10 x 60 x 60 = 36000

Distance covered in one hour= 36000 x 2.2 = 79200 m /hour

Speed of the car in km/hour = `79200/1000 = 79.2` km / hour

Speed = 79. 2 km / hr

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