Question 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 = (𝑇𝑜𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒)/(𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑐𝑜𝑣𝑒𝑟𝑒𝑑 𝑖𝑛 1 𝑟𝑒𝑣𝑜𝑙𝑢𝑡𝑖𝑜𝑛)
Diameter of circle = 80 cm
radius = r = 80/2 = 40 cm
Distance covered in one revolution = Circumference of wheel
= 2 𝜋r
= 2 ×𝜋×40
= 80π cm
Now, we find total distance covered
We know that,
Speed = 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒/(𝑇𝑖𝑚𝑒 )
Here, Speed = 66 km/hr
Time = 10 minutes = 10/60 hour = 1/6 hour
Putting value in formula
66 = Distance/(1/6)
66 ×1/6 = Distance
11 = Distance
Distance = 11 km
Distance = 11 km
= 11 × 1000 m
= 11000 m
= 11000 ×100 cm
= 1100000 cm
Now ,
Number of revolutions = (𝑇𝑜𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒)/(𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑐𝑜𝑣𝑒𝑟𝑒𝑑 𝑖𝑛 1 𝑟𝑒𝑣𝑜𝑙𝑢𝑡𝑖𝑜𝑛)
= 1100000/80π
= 110000/8π
= 110000/(8 × 22/7)
= (110000 × 7)/(8 × 22)
= 4375
Hence, number of revolutions = 4375

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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