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Q.

A boy is cycling such that the wheels of the cycle are making 140 revolutions per minute. The diameter of the wheel is 60 cm. Calculate the speed per hour with which the boy is cycling.


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a

15.84 km/hr

b

440 km/hr

c

7.5 km/hr

d

60km/hr 

answer is A.

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Detailed Solution

It is given that a boy is cycling such that the wheels of the cycle are making 140 revolutions per minute. The diameter of the wheel is 60 cm.
We need to calculate the speed per hour with which the boy is cycling.
We know that the circumference of a circle with radius r units is 2πr units.
We also know that d=2r.
Therefore,
Circumference = πd units
In this case, the distance the boy covers is equal to the product of the circumference of the wheel and the number of revolutions.
Therefore,
Distance covered=Circumference×Number of revolutions
Distance covered=πd×140
Distance covered=227×60×140
Distance covered=26,400 cm
We know that 1km=1,00,000cm
26,400cm=0.264km
We know that 1 min= 160 hours.
We know that,
Speed=Distance coveredTime taken
Speed=0.264(160)
Speed=0.264×60
Speed=15.84km/hr
Therefore, the speed per hour with which the boy is cycling is 15.84km/hr.
Hence, the correct option is 1.
 
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A boy is cycling such that the wheels of the cycle are making 140 revolutions per minute. The diameter of the wheel is 60 cm. Calculate the speed per hour with which the boy is cycling.