The moving walkway is a 300-foot long conveyor belt that

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The moving walkway is a 300-foot long conveyor belt that [#permalink]

23 Sep 2007, 23:21

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The ‘moving walkway’ is a 300-foot long 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 combined rate (including both walkway and foot speed) of 6 feet per second, reaches the group of people, and then remains stationary until the walkway ends. What is Bill’s average rate of movement for his trip along the moving walkway?

2 feet per second
2.5 feet per second
3 feet per second
4 feet per second
5 feet per second

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23 Sep 2007, 23:59

Bill approahces the group at 6 ft per second, but the group is also moving away from him at 3ft per second. So Bill needs to close the gap of 120 ft at 3 ft per second.

This will take 120/3 = 40 seconds. In 40 seconds, the group would have moved another 120 ft from where they were. So they're now 240 ft from the start.

So Bill's journey on the belt looks like this:

240 ft--> 6 ft per second --> Time = 40 seconds
60 ft --> 3 ft per second --> Time = 20 seconds

Average speed = 300/60 = 5 ft per second.

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Re: PS: Conveyner walkway [#permalink]

24 Sep 2007, 00:36

carpeD wrote:

Ive seen this somewhere. Anyway forget the conveyor belt speed for now.

Bills speed is 3ft per sec. so T=D/R T=120/3 ---> T1=40sec.

However, note that in this 40 sec bill didn't just travel 120 feet. He actually traveled 240feet. You have to count the 3ft per sec of the conveyor belt now. I just ignored that speed to make things easier to calculate.

So he has 60feet left @3ft per sec. T2=60/3 = 20 sec.

Now average Rate = Total D/ Total Time

300ft/(40+20)sec ---> 300/60 = 5ft per/sec.

E.

Re: PS: Conveyner walkway [#permalink] 24 Sep 2007, 00:36

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