Area/Perimeter of Circle

Chapter 12 Class 10 Areas related to Circles
Concept wise

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Ex 12.1, 4 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? Number of revolutions = (πππ‘ππ πππ π‘ππππ)/(π·ππ π‘ππππ πππ£ππππ ππ 1 πππ£πππ’π‘πππ) Diameter of circle = 80 cm radius = r = 80/2 = 40 cm Distance covered in one revolution = Circumference of wheel = 2 πr = 2 ΓπΓ40 = 80Ο cm Now, we find total distance covered We know that, Speed = π·ππ π‘ππππ/(ππππ ) Here, Speed = 66 km/hr Time = 10 minutes = 10/60 hour = 1/6 hour Putting value in formula 66 = Distance/(1/6) 66 Γ1/6 = Distance 11 = Distance Distance = 11 km Distance = 11 km = 11 Γ 1000 m = 11000 m = 11000 Γ100 cm = 1100000 cm Now , Number of revolutions = (πππ‘ππ πππ π‘ππππ)/(π·ππ π‘ππππ πππ£ππππ ππ 1 πππ£πππ’π‘πππ) = 1100000/80Ο = 110000/8Ο = 110000/(8 Γ 22/7) = (110000 Γ 7)/(8 Γ 22) = 4375 Hence, number of revolutions = 4375