The wheel of a motorcycle, 70 cm in diameter makes 40 revolutions in every 10 seconds. What is the speed of the motorcycle in km/hr Choose the correct choice from the following answers:
A) 30.68 km/hr  B) 31.68 km/hr  C) 32.68 km/hr  D) 33.68 km/hr  E) None of these
Explanation:   In this type of question, we will first calculate the distance covered in given time.   Distance covered will be, Number of revolutions * Circumference   So we will be having distance and time, from which we can calculate the speed. So let solve.   Radius of wheel = 70/2= 
<gadget id="calculator">70/2</gadget>
<output>35</output>
35 cm   Distance covered in 40 revolutions will be   40 * Circumference=40 * 2*\pi*r =40∗2∗22/7∗35=8800cm   =8800/100= 
<gadget id="calculator">8800/100</gadget>
<output>88</output>
88m   Distance covered in 1 sec=88/10= 
<gadget id="calculator">88/10</gadget>
<output>44/5 = around 8.8</output>
8.8m   Speed=8.8m/s=8.8∗18/5=31.68km/hr   Option 31.68 km/hr
<result>B</result>
The wheel of a motorcycle, 70 cm in diameter makes 40 revolutions in every 10 seconds. What is the speed of the motorcycle in km/hr