Question:
The radius of the wheel of a vehicle is 42 cm. How many revolutions will it complete in a 19.8-km-long journey?
Solution:
Radius of the wheel = 42 cm
Circumference of the wheel $=2 \pi \mathrm{r}$
$=2 \times \frac{22}{7} \times 42$
$=264 \mathrm{~cm}$
$=\frac{264}{100} \mathrm{~m}$
$=2.64 \mathrm{~m}$
Distance covered by the wheel in 1 revolution = 2.64 m
Total distance = 19.8 km or 19800 m
$\therefore$ Number of revolutions taken by the wheel $=\frac{19800}{2.64}=7500$
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