   What is the sum of the lengths of two trains that will protrude from the tunnels at the exact moment that they collide?

75 views

Two trains, each two miles long, enter two one mile long tunnels that are two miles apart from one another on the same track. The trains enter the tunnels at exactly the same time. The first train is going 5 miles/hour, and the second train is going 10 miles/hour. What is the sum of the lengths of the two trains that will protrude from the tunnels at the exact moment that they collide, assuming that neither train changes its speed prior to collision? The trains are on the same track headed in opposite directions (i.e. directly toward one another). posted Sep 28, 2015

2/3 miles

Distance between trains- 2+1+1=4 miles
Effective speed- 5+10=15 miles/hr
Time to collision- 4/15 hr
First trains travel before collision- 5*4/15=4/3 miles
Second trains travel- 10*4/15=8/3 miles
As the first train travels the distance less than it's length- 2-4/3= 2/3 miles will prorude
Second train travels more than it's lengths so no protrusion. So total length to protrude is 2/3 miles  answer Jul 30, 2018

Similar Puzzles

Two trains 132 metres and 108 metres in length are running towards each other on parallel lines , one at the rate of 32 km per hour and another at 40 km per hour .
In what time will they be clear of each other from the moment they meet ?

The distance between two stations is 400km. Two trains start simultaneously from these stations on parallel tracks to cross each other. The speed of one of them is greater than the other by 5 km/hr. If the distance between the two trains after two hours of their start is 170 km, find the speed of each train?

Accidentally, two trains are running in the opposite direction and enter a tunnel that is 200 kms long. A supersonic bird that has fled the lab and taken shelter in the tunnel starts flying from one train towards the other at a speed of 1000 kmph. As soon as it reaches the second train, he starts flying back to avoid collision and meets the first train again at the other end. The bird keeps flying to and fro till the trains collide with each other.

What is the total distance that the supersonic bird has traveled till the trains collided?

+1 vote

Two trains each 333 meter long, are running in opposite directions on parallel tracks.
If their speeds are 45 km/hr and 66 km/hr respectively, then what is the time taken by the faster train to pass the driver of slower one?