CDS 2015 PYQ with Answer — A boy is cycling such that the wheels of the cycle are making 140 rev…

2015 · Q55

A boy is cycling such that the wheels of the cycle are making 140 revolutions per minute. If the radius of the wheel is 30 cm, the speed of the cycle is

Elementary MathematicsMensuration

A15.5 km/hour
B15.84 km/hour
C16 km/hour
D16.36 km/hour

Explanation

This is a circular-motion unit-conversion problem. Each revolution covers one circumference: 2π × 0.3 m = 0.6π m, so 140 revolutions per minute give 84π m/min. Converting to km/h: 84π × 60/1000 = 5.04π km/h, and with π = 22/7 this equals 15.84 km/h. Option (c) 16 km/h is the rounded trap; the exact computation with 22/7 lands on 15.84. Hence option (b).