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 = (πππ‘ππ πππ π‘ππππ)/(π·ππ π‘ππππ πππ£ππππ ππ 1 πππ£πππ’π‘πππ)
Diameter of circle = 80 cm
radius = r = 80/2 = 40 cm
Distance covered in one revolution = Circumference of wheel
= 2 πr
= 2 ΓπΓ40
= 80Ο cm
Now, we find total distance covered
We know that,
Speed = π·ππ π‘ππππ/(ππππ )
Here, Speed = 66 km/hr
Time = 10 minutes = 10/60 hour = 1/6 hour
Putting value in formula
66 = Distance/(1/6)
66 Γ1/6 = Distance
11 = Distance
Distance = 11 km
Distance = 11 km
= 11 Γ 1000 m
= 11000 m
= 11000 Γ100 cm
= 1100000 cm
Now ,
Number of revolutions = (πππ‘ππ πππ π‘ππππ)/(π·ππ π‘ππππ πππ£ππππ ππ 1 πππ£πππ’π‘πππ)
= 1100000/80Ο
= 110000/8Ο
= 110000/(8 Γ 22/7)
= (110000 Γ 7)/(8 Γ 22)
= 4375
Hence, number of revolutions = 4375

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Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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