Book: NCERT - Mathematics
Chapter: 12. Areas Related to Circles
Subject: Maths - Class 10th
Q. No. 4 of Exercise 12.1
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The wheels of a car are of diameter 80 cm each. How many complete revolutions does each wheel make in 10 minutes when the car is travelling at a speed of 66 km per hour?
Diameter of the wheel of the car = 80 cm
Radius (r) of the wheel of the car = 40 cm
Circumference of wheel = 2πr
= 2π (40) = 80π cm
Speed of car = 66 km/hour
= 
cm/min
= 110000 cm/min
Distance travelled by the car in 10 minutes
= 110000 × 10 = 1100000 cm
Let the number of revolutions of the wheel of the car be n
n × Distance travelled in 1 revolution (i.e., circumference)
= Distance travelled in 10 minutes
n * 80 π = 1100000
n = 
= 
= 4375
Therefore, each wheel of the car will make 4375 revolutions
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