Aptitude - Problems on Trains - Discussion

T = 15 Sec.
T+100 = 25 Sec.
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T = 100/10 = 10 m/s where 10 sec. = 25-10(difference).
T = Length of the train
T = 15 Sec.*10 m/s=150 m.

Length of the train = 150 m.

Speed*Time = Distance.

S*T = D.

T = 25-15 = 10.

S = D/t = x/15, x = length of train.

(x/15)*10 = 100.

x = 150m.

Speed = Length/Time.....(1).

Distance = Speed*Time.....(2).

Time = Higher time - Lower time.

= 25-15 = 10.

Distance = 100 given.

100 = Speed*10.

Speed = 10 substitute in equation (1).

Length = 10*15 = 150.

Why 25-10?

Let the speed of the train be x.

Then, the length of the train is 15x.

Therefore, 100+15x = 25x.

x = 10.

Which mean the speed of the train is 10 m/s as assumed above.

Then the length of train is 150 m.

Let speed = X; then length of train = 15 X;

Hence (15X+100)/X = 25.

Answer the length of train is 15X = 10*15 = 150.

Let the length of the train= l meters.

We know speed = length/ time.
So, speed of the train = l/15 m/sec.

To cross the platform the train have to cover = length of the train + length of the platform [ this is the relative distance].

So total length = l+100.

l+100=(l/15)*25 [applying the rule:- length = speed*time.
=> l+100= 25l/15 m.
=> l+100= 5l/3 m.
=> 3l+300= 5l m.
=> 5l-3l= 300 m.
=> 2l=300 m.
=> l= 150 meters.

The length of the train is 150 meters.

If a train crosses 300 metres long platform in 38 seconds while it crosses a signal pole in 18 seconds. What is the speed of the train in km/h?

Please tell me the answer.

Let,
Length(distance) of the train = x meters.
Here time = 15 sec.

We know, Speed = d/t
=> x/15 m/sec.
Then,
100 + x = x
----------------------------
25 15
25x = 1500 + 15x.
25x - 15x = 1500
10x = 1500
x = 150 meters ==>answer.