Aptitude - Problems on Trains - Discussion
Discussion Forum : Problems on Trains - General Questions (Q.No. 10)
10.
A jogger running at 9 kmph alongside a railway track in 240 metres ahead of the engine of a 120 metres long train running at 45 kmph in the same direction. In how much time will the train pass the jogger?
Answer: Option
Explanation:
Speed of train relative to jogger = (45 - 9) km/hr = 36 km/hr.
| = |  |
36 x | 5 |  m/sec |
| 18 |
= 10 m/sec.
Distance to be covered = (240 + 120) m = 360 m.
 Time taken = |
|
360 | sec |
= 36 sec. |
| 10 |
Discussion:
106 comments Page 8 of 11.
Saurav said:
1 decade ago
Relative speed itself means that the speed of other object is 0. As we are finding the speed of the train relative to man. (45-9 = 36). So man has been made to be in rest.
Hari said:
1 decade ago
You asked the question for cross the jogger only, but you calculate for the platform, please give me the explanation.
Preethi said:
1 decade ago
@Dhanu: Initially when I read the question I also followed your concept. But relative speed is a different concept. When you are considering relative speed the distance traveled by the jogger is also considered hence only the initial distance which has to be traveled alone is enough to calculate the time required. Where as when you do chocolate method I mean work and time problem you can apply the concept.
Prerna said:
1 decade ago
Do we suppose to pass the platform too. If jogger is also moving there is no point in considering the jogging track length.
Relative speed is 10 m/s hence to pass the train of length 120m we will need only 12 sec.
Relative speed is 10 m/s hence to pass the train of length 120m we will need only 12 sec.
Jay said:
1 decade ago
Relative speed concept when two object moves in same direction than their speed is equal to the subtraction of their actual speed. Relative speed is a speed of one object with respect to another ok.
Neel said:
1 decade ago
Thus now the total distance covered by train is 240+120 only.
Neel said:
1 decade ago
We subtract 45-9 so as to make the position of the jogger to be the reference position. By subtracting that the jogger is stationary now.
Raju Pathro said:
1 decade ago
We can add jogger length also but it is neglected when compare with train.
Amresh said:
1 decade ago
Total distance should be= 120+240+x.
Maulik Dodia said:
1 decade ago
But I can not understand, that the tain have to pass the only 120m distance w.r.t the jogger. Not 240? Isn't it? Can anyone explain me that?
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