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 4 of 11.
Neel said:
1 decade ago
Thus now the total distance covered by train is 240+120 only.
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.
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.
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.
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.
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.
Vedant said:
1 decade ago
@People considering distance traveled by jogger.
240 + 120 + 9*A (5/18) / (45*5/18) = A.
This will give A=36 so given solution is correct do no take relative speed concept just simply add distance to be covered and divide by train speed.
240 + 120 + 9*A (5/18) / (45*5/18) = A.
This will give A=36 so given solution is correct do no take relative speed concept just simply add distance to be covered and divide by train speed.
Ramsha said:
1 decade ago
Yes @Vedant, I also get the same answer through the same process.
Atoria M. Horace said:
1 decade ago
I still can't understand how the 5/18 came about.
Prashant said:
1 decade ago
Please clear my doubt.
Let the train pass after t time.
So train has to cover (120+240+x)/45 in t time.
And jogger covers x/9 in t time.
(120+240+x) /45 = x/9.
Answer is 90 sec but logic is correct that they both meet after t time.
Let the train pass after t time.
So train has to cover (120+240+x)/45 in t time.
And jogger covers x/9 in t time.
(120+240+x) /45 = x/9.
Answer is 90 sec but logic is correct that they both meet after t time.
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