Question

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

• A. $4363$
• B. $4376$
  
• C. $4375$
• D. None of these

Answer 1

Answer: (C)

$4375$

Given,
speed of the car is $66km/hr$
Therefore,
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=$80cm$
Therefore,
radius of car wheel=$\frac{diameter}{2}$
=$\frac{80}{2}cm$
=$40cm$
Therefore,
Circumference of car wheel=$2\pi r$
=$2\times \frac{22}{7}\times 40$
=$\frac{1760}{7}cm$
Therefore,
Number of revolution made by the wheels in $10$minutes=$\frac{\text{distance covered by the car in 10 minutes}}{\text{distance travelled by the car when its wheel completes one revolution}}$

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

=$\frac{77\times 1000\times 100cm}{1760}$
=$4375$ revolutions.