Question

A train 100m long is to cross a river bridge of length 800 m. What time will it take to cross the bridge? Given that the train moves with a constant velocity of 36 km/h.

Answer 1

Answer :-

90s

Explanation :-

Given :

Length of the train = 100m

Length of the bridge = 800m

Constant velocity of the train = 36km/h

To Find :

Time taken by the train to cover the whole bridge = ?

Solution :

First up all let’s convert speed into m/s

$\sf{}\implies \dfrac{36\times 1000}{1\times 60\times60}$

$\sf{}\implies \dfrac{36000}{3600}$

$\sf{}\therefore 10m/s$

Therefore,speed of the train is 10m/s

(Refer to the attachment)

Total distance covered by the train is from point A to C.Let’s assume train has begun from point A and come to the point B, but still it has not crossed the whole bridge, as the train started from its end, after completing its whole ending portion then only we can say that the train has crossed the bridge.

Therefore, after travelling the whole distance of the bridge, the train will cover its distance to cross the whole bridge.

Total distance travelled = Length of the bridge + Length of the train  

⇒ 800m + 100m

∴ 900m

We know,

$\boxed{\sf{}Speed=\dfrac{Distance}{Time\ taken}}$

So,

$\boxed{\sf{}Time\ taken=\dfrac{Distance}{Speed}}$

Put their values and find out “Time”

$\sf{}\implies \dfrac{900m/s}{10s}$

$\sf{}\therefore 90s$

Therefore,time taken by the train to cross the whole bridge is equal to 90s

Answer 2

Diagram :

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Answer:

• Velocity (v) = 36 km/hr = 10 m/s
• Length of train = 100 m
• Length of bridge = 800 m

Therefore, The total distance travelled by train is :

• Length of bridge + Length of train = 100 + 800 = 900 m

• Thus, Total Distance (d) = 900 m

☯ $\underline{\boldsymbol{According\: to \:the\: Question\:now :}}$

$:\implies \sf Time = \dfrac{Distance}{Velocity}$

$:\implies \sf Time = \dfrac{900}{10}$

$:\implies \underline{ \boxed{\textsf{ \textbf{ Time = 90 seconds}}}}$

$\therefore\underline{\textsf{ Time taken by the train to cross the bridge is {\textbf{90 seconds}}}}.$