Moving Walkway Problem

[afashoro]

Problem:
The "˜moving walkway’ is a 300-foot long walkway consisting of a conveyor belt that moves continuously at 3 feet per second. When Bill steps on the walkway, a group of people that are also on the walkway stands 120 feet in front of him. He walks toward the group at a rate of 3 feet per second. Once Bill reaches the group of people, he stops walking and stands with them until the walkway ends. What is Bill’s average rate of movement for his trip along the moving walkway?

My Question: When it comes to calculating Bill's speed when he is walking, why don't we explicitly take into account the 3ft/s that the belt is moving (i.e. double his speed to 6 ft/s during the time he is catching up to the crowd)? Is it because everyone is moving at that speed and you discount the speed of the belt (since technically the crowd ahead of him is not moving any additional distance beyond the conveyor belt's 3 ft/s)?

[mschwrtz]

If you want to ask about an element of the explanation, please post as much of the explanation as is necessary to make that question clear. Also, there are 16 other threads on this same question, so check the archives.

That looks more brusque on the screen than I mean it to, but check out the archives, and if you don't find your answer, bump the best of the threads with a quote from the explanation that confused you.

Good luck, Michael