Diameter of a car wheel is 21 cm. A car driver moving at the speed of 66 km/hr takes 36 seconds to reach a destination. How many revolutions will the wheel make during the journey?
Diameter of wheel = 21 cm
=> Circumference of wheel = Distance travelled in 1 revolution = $$2\pi r$$
= $$2\times\frac{22}{7}\times\frac{21}{2}=66$$ cm
Speed of car = 66 km/hr = $$(66\times\frac{5}{18})=\frac{55}{3}$$ m/s
Total distance travelled by car = $$\frac{55}{3}\times36=660$$ m = $$66000$$ cm
$$\therefore$$ Total revolutions taken by the wheel = $$\frac{66000}{66}=1000$$
=> Ans - (D)
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