In detail

Trains in the tunnel

Trains in the tunnel

A 400-meter-long train crosses a 600-meter-long tunnel at the same time when another train twice as fast and half-length crosses a triple-length tunnel.

Which train will (completely) leave the tunnel first?

Solution

If we apply the formula: speed = space / time We have the time it takes for the first train to completely exit the tunnel is:

For the second train of half length: 200m, triple tunnel length: 1800 and twice the speed: 2v we have to:

In other words, it takes exactly the same to get out of the tunnel.