Question

A train crosses two bridges 215 m
and 275 m long in 15 and 18 s
respectively. Find the length of the
train (m).​

Answer 1

case 1:

T……………..(l m)………………..B………………(430 m)………………….R

30 sec

case 2:

T……………..(l m)……………….B………………..(550 m)…………………R

36 sec

Make l m long train as a point train ‘T’.

Thus in case 1,

Our point train T has to travel total (l+430)m.

Let ‘s’ be the speed of the train.

Thus using speed=distance/time.

s=(l+430)/30

and from case 2,

s=(l+550)/36

as same train is crossing both the bridges.

therefore,

(l+430)/30=(l+550)/36

by solving above equation,

l=170 m.

Thus the length of the train is 170 m.

from case 1,

Thus speed (s)=(170+430)/30

=600/30

=20 m/s

Thus the speed of the train is 20 m/s.