Question

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

Answer 1

Given, speed of the car is $66km/hr$

Distance travelled by the car in $1hr=66km/hr$

Distance travelled by the car in $10mins=\frac{66}{60}\times 10km$

$=11km=11\times 1000m=$$11\times 1000\times 100cm$

Diameter of car wheel $80cm$

radius of car whee,l

$r=\frac{\text{diameter}}{2}$

$\Rightarrow r=\frac{80}{2}cm$

$\Rightarrow r=40cm$

Circumference of car wheel,

$C=2\pi r$

$\Rightarrow C=2\times \frac{22}{7}\times 40$

$\Rightarrow C=\frac{1760}{7}cm$

Now,

Number of revolution made by the wheels in $10$ minutes=$=\frac{\text{distance covered by the car in 10 minutes}}{\text{distance travelled by the car when its wheel completes one revolution}}$

$=\frac{11\times 1000\times 100cm}{\frac{1760}{7}}$

$=\frac{77\times 1000\times 100cm}{1760}$

$=4375$

Hence, required number of revolutions are $4375$.