Question

3. A person is standing on a railway bridge
which is 50 metres long. He finds that a
train crosses the bridge in 4 Va seconds
but himself in 2 seconds. Find the length
of the train and its speed in km per hour.
​

Answer 1

the speed of the train is 90kmph

and the length of the bridge is 50mts

Answer 2

Answer:

A man is standing on a railway bridge which is 180m long. he finds that a train crosses the bridge in 20 sec but himself in 8 sec, the length of the train is $50m$ and its speed is $90km/h$

Step-by-step explanation:

• The speed (V) of a body is the distance(d) covered by it divided by the time taken (t) to cover the distance

        $V=d/t$

From the question,

time taken to cross the man $t'=2s$

the length of the train is the distance crossed, let it be x

⇒the velocity of the train $V=x/2$ (equation 1)

length of the bridge $l=50m$

so total distance covered is $x+50$

time to cross this distance is $t=4s$

the velocity of the train $V=\frac{x+50}{4}$ (equation 2)

velocity is same so equate the two equations

⇒$x/2=\frac{x+50}{4}$

$4x=2x+100\\ 2x=100\\x=50m$

⇒length of the train $x=50m$

speed of the train

$V=x/8=50/2=25m/s\\V=25*18/5=90km/h$