Question

A train runs at a speed of 42 m/s and takes 35 seconds to pass a tunnel. after travelling some distance, it takes 15 seconds to pass a pole. what is the length of the tunnel?

Answer 1

So,

While passing the tunnel it takes 35sec

Displacement = Velocity × Time

Therefore,

L(Train) + L(Tunnel)

= 42 × 35 = 1470m

Now,

It takes 15 sec to pass a pole

So,

L(Train)

= 15×42= 630m

L(Tunnel) = 1470 - 630 = 840

So,

The length of tunnel is 840m

Answer 2

Acc to the question,

Speed of the train = 42m/s

Time taken to pass the tunnel = 35s

Therefore, Total distance covered = Speed x Time = 42 x 35 = 1470m

Now, we should be aware that this distance covered is not just the length of the tunnel but combined length of train and tunnel.

Now time taken to pass the pole = 15s.

Length of the train = Distance covered while passing the pole = 42 x 15 = 630m.

Therefore, Length of tunnel = Combined length of train and tunnel - Length of train = 1470 - 630 = 840m (Ans)