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 1 of 11.
Karthik said:
2 decades ago
Y DID U substract 45-9? i didn't understand
RPrabha said:
2 decades ago
If in both the objects move in the same direction, the relative speed would be the sum of both the speeds. How is calculation is done. Even if tried with the mentioned procedure, the options don't have the derived answer
Ramesh karthick said:
2 decades ago
Jogger is not idle. He also running. So we done this step 45-9km/hr.
9km/hr is jogger speed.
9km/hr is jogger speed.
Karthik said:
2 decades ago
Relative speed= hidh speed + low speed when the objects are moving in the oppsite direction
Relative speed= hidh speed - low speed when the objects are moving in the same direction
Relative speed= hidh speed - low speed when the objects are moving in the same direction
Sarika said:
2 decades ago
Yes, karthik is right.
Chetan said:
2 decades ago
Relative speed means speed of an object w.r.t to another object.
Tips:
1.)Two objects moving in same direction-->stop object 2 and subtract object 2' s speed from object 1.
Ex: Suppose two cars moving in same direction with 60 kmph(both cars same speed)..it is obvious that relative speed is 0 kmph....how did it come??? by subtracting..ok.
2.) Two objects moving in oppsite direction--->stop obj 2 and add its speed to obj1.
Ex:
Car1 speed=40 kmph in east direction.
Car2 speed=50 kmph in west direction.
Relative speed of car1 w.r.t car2 is
stop car2, add its speed to car1, i.e 40+50 = 90.
Tips:
1.)Two objects moving in same direction-->stop object 2 and subtract object 2' s speed from object 1.
Ex: Suppose two cars moving in same direction with 60 kmph(both cars same speed)..it is obvious that relative speed is 0 kmph....how did it come??? by subtracting..ok.
2.) Two objects moving in oppsite direction--->stop obj 2 and add its speed to obj1.
Ex:
Car1 speed=40 kmph in east direction.
Car2 speed=50 kmph in west direction.
Relative speed of car1 w.r.t car2 is
stop car2, add its speed to car1, i.e 40+50 = 90.
Priyanka said:
1 decade ago
Can you explain me why in this question relative speed is subtaction of higher speed to lower while in same direction relative speed is addition of both object speed?
Jelli said:
1 decade ago
Hi
i think you can use the formula
u=(a+b)/(u-v) (both in a same dir)
=(120+240)/(45-9)*5/18
=36s
i think you can use the formula
u=(a+b)/(u-v) (both in a same dir)
=(120+240)/(45-9)*5/18
=36s
Sumi said:
1 decade ago
hi priyanka u understood wrongly relative speed for the objects in same direction is obtained by subtracting only
Dheeraj said:
1 decade ago
@rprabha... no when two things are going in same direction then realtive speed is not sum of that things..
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