Question

The wheel of a motorcycle, $70cm$ in diameter, makes $40$ revolutions in every $10$ seconds. What is the speed of the motorcycle in km/hr?

• A. $22.32$
• B. $27.68$
• C. $31.68$
• D. $36.24$

Answer 1

The correct option is C $31.68$

Answer is C.
We will first calculate the distance covered in given time.
Distance covered = Number of revolutions $\times$ Circumference
So, we will be having distance and time, from which we can calculate the speed.
Radius of wheel = 70/2 = 35 cm.
Distance covered in 40 revolutions will be = 40 $\times$ Circumference.
That is,
$40\times 2\pi r=40\times 2\times 3.14\times 35=8800cm=88m$.
Distance covered in 1 second = 88/10 = 8.8 m.
Therefore, speed = 8.8 m/s.
That is, $88\times \frac{18}{5}=31.68km/hr$.
Hence, the speed of the motorcycle is 31.68 km/hr.