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Question
The wheel of a motor cycle is of radius 35 cm. How many revolutions per minute must the wheel make so as to keep a speed of 66 km/hr ?
Solution
Given, radius of wheel, r = 35 cm
Circumference of the wheel
= 2πr
= `2 xx 22/7 xx 35 "cm"`
= 220 cm
But speed of the wheel
= 66 km/h–1
= `(66 xx 1000)/60` m/min
= 1100 × 100 cm/min–1
= 110000 cm/min–1
∴ Number of revolutions in 1 min
= `(110000)/220`
= 500 revolutions
Hence, the required number of revolutions per minute is 500.
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