Question

The wheels of a car are of diameter $80$ cm each. How many complete revolutions does each wheel make in $10$ minutes when the car is travelling at a speed of $66$ km per hour?

Answer 1

Diameter of the wheels of a car $=80$ cm
$\Rightarrow \text{radius}=40$ cm
Circumference of each wheel$=2\pi r=2r\times \pi =80\pi$cm [Since diameter $d=2r$]

Now,
Speed of the car = $66$ km/hr = $66\times \frac{100000}{60}$ cm/min

Distance = Speed $\times$ Time taken

Distance travelled by car in 10 minutes will be
$=66\times \frac{100000}{60}\times 10$
$=11\times 100000$
$=1100000$ cm

Now,

No. of revolutions taken $=\frac{\text{Distance travelled by car}}{\text{Circumference of wheels}}$

$\Rightarrow$ No. of revolutions taken in $10$ minutes $=\frac{1100000}{80\pi }$
$=\frac{(1100000\times 7)}{(80\times 22)}$
$=4375$
Hence, each wheel makes $4375$ complete revolutions in $10$ minutes.