Q1. If the wheel of a train engine, with a circumference of \(\frac{30}{7}\) metres, makes 7 revolutions in 6 seconds, then the speed of the train, in km/hr, is:
A 27
B 18 Correct
C 20
D 25
Explanation
In one revolution, the wheel covers a distance equal to its circumference, \(\frac{30}{7}\) metres. In 7 revolutions, it covers \(7 \times \frac{30}{7} = 30\) metres. This distance is covered in 6 seconds, so the speed is 5 m/s. Converting metres per second to kilometres per hour gives \(5 \times \frac{18}{5} = 18\) km/hr. The values 27, 20 and 25 do not match this conversion from the given distance and time.