Question

The wheels of a car are of diameter 80cm each. how many complete revolution does each wheel make it in 10 minutes when the car is traveling at a speed of 66 km/hr

Answer 1

First, Convert 66 kmph into m/s i.e 66*1000/3600 = 66*5/18= 55/3 m/s.
Now, Distance covered in 10 min = (55/3*10*60)m = 11,000 m.
Circumference of wheel= (22/7*80/100 )m , which is distance covered in one Revolution.
No. of complete Revolution = 11000/(22/7*80/100 ) = 4,375.

Answer 2

Radius of wheel= 80/2 = 40cm
∴ The distance travelled in one revolution is = 2πr = 2 x 22/7 x 40 = 1760/7 cm.
 
speed of car= 66km/hr= 66 x 1,00,000/60 cm/min = 1,10,000 cm/min.
distance covered by car in 1 min = 1,10,000cm
distance covered by car in 10min =  110,000 x 10 = 11,00,000cm.

number of complete revolution =
               distance covered in 10min / distance covered in one revolution.
= 11,00,000/ 1760/7 
                      = 11,00,000/1 x 7/1760 = 4375 revolutions.

Hence, in 10min each wheel of car makes 4375 revolutions.