About Me
I've got a masters degree in computer science and over 10 years of experience building web-based systems using Java/J2EE, Ruby, Rails and PHP. I'm a strong believer in the effectiveness of Agile Methods. Read more »Subscribe
I've got a masters degree in computer science and over 10 years of experience building web-based systems using Java/J2EE, Ruby, Rails and PHP. I'm a strong believer in the effectiveness of Agile Methods. Read more »
Two Trains
The Problem
One train leaves Los Angeles at 15mph heading for New York. Another train leaves from New York at 20mph heading for Los Angeles on the same track. If a bird, flying at 25mph, leaves from Los Angeles at the same time as the train and flies back and forth between the two trains until they collide, how far will the bird have traveled?
The Solution
At first blush this seemed like a limit problem. But it’s not. It’s a vector problem. Sum the train vectors. The trains will collide in the amount of time it takes to travel the distance between them (d) at 35mph. So, we end up with a term t = d/35. The only important part about the bird is that it travels at a constant speed, 25mph. So the amount of distance covered by the bird will be the how far it can go in time t at 25mph. So, the solution to this, d’, the distance traveled by the bird is 25 * t. To put all that together, d’ = 25d/35.