A boy is cycling in such a way that the wheels of his bicycle are making 140 revolutions per minute.If the diameter of a wheel is 60cm,calculate the speed ( in km/ hr) at which the boy is cycling.
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Answer:
We have been given that a boy is cycling such that the wheels of the cycle are making 140 revolutions per minute. Also, the diameter of the wheel is 60cm, then, we have to find the speed per hour.
The diameter of a wheel is 60cm.
We know that radius is half of the diameter.
⇒Radius(r)=d2=602=30cm
We know that, circumference of a circle having radius 'r' is \(2\pi r.\)
Circumference of wheel(c)=2×π×30
Since, we know that \(\pi = \dfrac{{22}}{7}\)
Circumference of wheel(c)=2×227×30⇒188.57cm
Now, the speed of the wheel will be equal to the product of revolution per second and circumference of the wheel.
⇒Speed=140×188.57cm minute⇒26399.8cm minute
Now, we have to find the speed in km per hour, so, we will have to convert cm into km and minute to hour by using the following conversion,
1cm=10−5km1 minute=160hour
⇒Speed=23699.8×10−5160⇒23699.8×60×10−5km/hr⇒1583988×10−5km/hr⇒15.84km/hr(approximately)
Therefore, the speed in km per hour with which the boy is cycling is equal to 15.84km/hr.
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