A train traveling at 100 kmph overtakes a motorbike traveling at 64 kmph in 40 seconds. What is the length of the train in meters?  Answers.
A) 1777 meters B) 1822 meters C) 400 meters D) 1111 mete E) None of these
Answer   Concept : Distance covered by train when it crosses a moving object   When a train overtakes another object such as a motorbike, whose length is insignificant compared to the length of the train, the distance traveled by the train is equal to the length of the train.   Because the motorbike is also moving, we have to take the relative speed between the train and the motorbike and not just the speed of the train.   The length of the train = distance traveled by the train while overtaking the motorbike = relative speed between the train and the motorbike * time taken   In this case, as both the objects i.e., the train and the motorbike are moving in the same direction, the relative speed between them = difference between their respective speeds = 100 - 64= 
<gadget id="calculator">100 - 64</gadget>
<output>36</output>
36 kmph.   Distance traveled by the train while overtaking the motorbike= 36 kmph * 40 seconds.   The final answer is in meters and the speed is given in kmph and the time in seconds.   So let us convert the given speed from kmph to m/sec.   1 kmph = 5/18 m/sec   Therefore, 36 kmph = 36 * 5/18= 
<gadget id="calculator">36 * 5/18</gadget>
<output>10</output>
10 m/sec.   Relative speed= 10 m/sec. Time taken = 40 seconds.   Therefore, distance traveled = 10 * 40= 
<gadget id="calculator">10 * 40</gadget>
<output>400</output>
400 meters.   400 metershoice 400 meters
<result>C</result>
A train traveling at 100 kmph overtakes a motorbike traveling at 64 kmph in 40 seconds. What is the length of the train in meters?