entered the platform

[sanju09]

A train of length 600 m is leaving a platform at 15 kmph. Before it completely left the platform, another train of length 300 m coming in the opposite direction with a speed of 75 kmph starts crossing the first train. The second train entered the platform completely, and simultaneously crossed the first train. If the length of the platform is 1,125 metres, then what is the time taken by the second train to cross the platform after it has crossed the first train?

1 kmph = 5/18 m/sec; 1 km = 1000 m, m for meters and sec for seconds.
kmph stands for km per hour.
A. 72 seconds
B. 60 seconds
C. 54 seconds
D. 48 seconds
E. 36 seconds

OA C if not badly worded, I hope

[sacx]

The question is basically asking how much time does it take train B to travel a distance equivalent to the length of the platform.

When the train B completely entered the platform it had already covered a distance of 300 mts so the remaining distance to cover = 1125 -300 = 825 mts

Now the train will have to cover 300 mts before it completely leaves the platform

So the total distance to cover = 825 + 300 = 1125 mts

S = d/t
75 * (5/18) = 1125/t (multiply by 5/18 to convert km/hr to m/s)

t = 54 secs