Question

What is the radius (in cm) of the tyre in a car, if it covers 0.396 km in 300 rotations? (Use π = $\frac{22}{7}$)

• A. 14 cm
• B. 21 cm
• C. 7 cm
• D. 28 cm

Answer 1

The correct option is B

21 cm

The circumference of the tyre = 2πr (Distance travelled in each rotation)

Total Distance = Distance covered in 1 rotation x Number of rotations

$\Rightarrow 0.396=2\times \frac{22}{7}\times r\times 300$

$\Rightarrow r=\frac{0.396\times 7}{2\times 22\times 300}$

Hence r = 0.00021 km or 21 cm.