Aptitude - Problems on Trains - Discussion

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.

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?

@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.

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.

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.

kmph=kilo meter per hour or km/hr

What is kmph?

Ya gayatri I agree with you.

@Viji.T
i agree with u .. by the time the train approaches the jogger he/she would have covered some additional distance...how is that even possible to take the sum (240+120) as the total distance travelled ignoring the the distance covered by the jogger in that time interval...

For the same direction we get relative speed by subtracting speeds.