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1. The diameter of the driving wheel of a bus is 140 cm. How many revolutions per minute must the wheel make in order to keep a speed of 66 km per hour?
- A. 200
- B. 200
- C. 200
- D. 200
Answer: Option B
Explanation:
Given :
The diameter of the driving wheel = 140 cm
Speed of a bus = 66 km/hr
Concept Used:
Circumference of a circle = 2πr
Number of revolutions of a wheel (N) = D/d
d = Distance traveled by the wheel in 1 revolution
Calculation:
Distance travelled by bus in 1 hour = 66km = 6600 meter
Distance travelled by bus in 1 minute = (66000)/60 = 1100m
Distance travelled by a wheel in 1 revolution = Circumference = 2πr
Put 2r = 140 cm , 1 m = 100 cm , π =22/7
Therefore,
Distance traveled by a wheel in 1 revolution = (22/7) × (140/100)
Distance traveled by a wheel 1 revolution = 4.40 m
Now, using the above formula
N × 4.4 = 100
N = 250
∴ The number of revolutions per minute is 250.
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