Question

A train, x meters long, traveling at a constant speed, takes 20 seconds from the time it first enters a tunnel 300 meters long until the time it completely emerges from the tunnel. one of the stationary ceiling lights in the tunnel is directly above the train for 10 seconds. find x

Answer 1

As the train is traveling at a constant speed, therefore the ratio of distance to time will be the same over any distance and respective time interval.

The train travels  $300+x$ m in 20 s.

As the stationary ceiling lights in the tunnel is directly above the train for 10 s, it means the train travels x m in 10 s, so in 20 s train travels 2 x m.

Therefore,

$300+x=2x$ $\Rightarrow  x =300m$

Hence, the length of the train is 300 m.