Aptitude - Problems on Trains - Discussion

kmph=kilo meter per hour or km/hr

Step 1 find train speed in m/s 45*5/18=10m/sec.

Length og train=speed*time.

120=10*x=12 sec.

But 240 more to covered then

240+120=10*x.

x=36 answer.

How can the distance be 240 + 120. Until the train's engine covers 240m in that time the jogger will also move some distance ahead. So the total distance is not 240+120.

@Manish kumar mina.

Yeah you are right. We are not finding the time w.r.t platform, its w.r.t the man, who is moving with 9kmph, so the total distance will be 120+0=120 and required time will be (120+0) / (45-9) =12 sec.

The total distance covered by the train when it passes by the jogger should be (120+240+distance covered by jogger during that time say "x") right?

So it will be
x = 9*(5/18)*T, where T is our required answer.
i.e x = 5/2*T m

And according to given details,

Relative speed = (45 - 9) km/hr = 36 km/hr.
i.e 10m/sec

T = ((120+240+x)/10 )seconds

Putting value of x = 5/2*T

T = ((120+240+(5/2)*T)/10 )
= ((360+(5/2)*T)/10 )

i.e

10*T = 360+2.5*T
7.5*T = 360
T = 48 seconds.

This should be also correct right?

Dhanu,

You are right. As the jogger is also in motion so its speed should be considered and that changes the time significantly. I wonder why no one have pointed this earlier.

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?

Total distance should be= 120+240+x.

We can add jogger length also but it is neglected when compare with train.

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.