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Ex 12.1, 4 - The wheels of a car are of diameter 80 cm each - Area/Perimeter of Circle

  1. Chapter 12 Class 10 Areas related to Circles
  2. Serial order 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 = (๐‘‡๐‘œ๐‘ก๐‘Ž๐‘™ ๐‘‘๐‘–๐‘ ๐‘ก๐‘Ž๐‘›๐‘๐‘’)/(๐ท๐‘–๐‘ ๐‘ก๐‘Ž๐‘›๐‘๐‘’ ๐‘๐‘œ๐‘ฃ๐‘’๐‘Ÿ๐‘’๐‘‘ ๐‘–๐‘› 1 ๐‘Ÿ๐‘’๐‘ฃ๐‘œ๐‘™๐‘ข๐‘ก๐‘–๐‘œ๐‘›) Diameter of circle = 80 cm radius = r = 80/2 = 40 cm Distance covered in one revolution = Circumference of wheel = 2 ๐œ‹r = 2 ร—๐œ‹ร—40 = 80ฯ€ cm Now, we find total distance covered We know that, Speed = ๐ท๐‘–๐‘ ๐‘ก๐‘Ž๐‘›๐‘๐‘’/(๐‘‡๐‘–๐‘š๐‘’ ) Here, Speed = 66 km/hr Time = 10 minutes = 10/60 hour = 1/6 hour Putting value in formula 66 = Distance/(1/6) 66 ร—1/6 = Distance 11 = Distance Distance = 11 km Distance = 11 km = 11 ร— 1000 m = 11000 m = 11000 ร—100 cm = 1100000 cm Now , Number of revolutions = (๐‘‡๐‘œ๐‘ก๐‘Ž๐‘™ ๐‘‘๐‘–๐‘ ๐‘ก๐‘Ž๐‘›๐‘๐‘’)/(๐ท๐‘–๐‘ ๐‘ก๐‘Ž๐‘›๐‘๐‘’ ๐‘๐‘œ๐‘ฃ๐‘’๐‘Ÿ๐‘’๐‘‘ ๐‘–๐‘› 1 ๐‘Ÿ๐‘’๐‘ฃ๐‘œ๐‘™๐‘ข๐‘ก๐‘–๐‘œ๐‘›) = 1100000/80ฯ€ = 110000/8ฯ€ = 110000/(8 ร— 22/7) = (110000 ร— 7)/(8 ร— 22) = 4375 Hence, number of revolutions = 4375

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Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He provides courses for Mathematics from Class 9 to 12. You can ask questions here.
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