Question

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. 

Answer 1

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