Question

A 660 m long train crosses a bridge and a pole in 1 min 25 sec and 11 sec respectively. What is the length of the bridge?​

Answer 1

Given :- A 660 m long train crosses a bridge and a pole in 1 min 25 sec and 11 sec respectively.

To Find :-

• What is the length of the bridge ?

Solution :-

Let us assume that, the length of the bridge is x m.

case 1) :- crossing a pole .

→ Distance = Length of train = 660 m .

→ Time = 11 seconds.

so,

→ Speed of train = D / T = (660/11) = 60 m / s.

case 2) :- crossing a bridge of x m.

→ Distance = Length of train + Length of bridge = (660 + x)m .

→ Time taken = 1 minute , 25 seconds = 60 + 25 = 85 seconds.

so,

→ speed = D / T = {(x + 660) / 85} m / s .

A/q,

→ 60 = (x + 660)/85

→ 60 * 85 = x + 660

→ x = 60 * 85 - 660

→ x = 5100 - 660

→ x = 4440 m (Ans.)

Hence, Length of bridge will be 4440 m.

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Answer 2

SOLUTION

GIVEN

A 660 m long train crosses a bridge and a pole in 1 min 25 sec and 11 sec respectively.

TO DETERMINE

The length of the bridge

EVALUATION

Here it is given that the 660 m long train crosses a bridge and a pole in 1 min 25 sec and 11 sec respectively.

Now when a train cross a pole , it only travels own length

Train is 660 m long and it takes 11 sec to cross the pole

So speed of the train

$\displaystyle \sf{ = \frac{660}{11} \: \: m/s }$

$\displaystyle \sf{ = 60\: \: m/s }$

Now 1 min 25 sec = 85 sec

So the distance covered in 85 sec

= 60 × 85 m

= 5100 m

Now we know that when a train cross a bridge , it travels own length + Length of the bride

So

$\sf{Length \: of \: the \: train + Length \: of \: the \: bride = 5100 \: m}$

$\sf{ \implies \: 660 \: m + Length \: of \: the \: bride = 5100 \: m}$

$\sf{ \implies \: Length \: of \: the \: bride = 5100 \: m - 660 \: m}$

$\sf{ \implies \: Length \: of \: the \: bride = 4440 \: m}$

FINAL ANSWER

The length of the bridge = 4440 m

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