Rate

[heshamelaziry]

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 combined rate (including both walkway and foot speed) of 6 feet per second relative to the ground. 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?

2 feet per second

2.5 feet per second

3 feet per second

4 feet per second

5 feet per second

OA

5

[Resurgent]

Good question. Tricky because we have to consider the distance covered when Bill is walking on the walkway.

Lets first find the time talken by Bill to reach the group that is standing 120feet away from him.
Since both Bill & the group are travelling at the standard speed of 3feet/sec, Bill's walking speed is (6-3) 3feet/sec. So, the time taken the reach the group is 120/3 = 40secs. Now, the actual distance covered by Bill (the speed relative to the ground is 6feet/sec) is: 6*40 = 240feet.

So, the remaining 60feet is travelled at 3feet/sec in 20secs.

So, the average speed is = Total distance/Total time taken ==> 300/(40+20) ==> 5feet/sec

Hope this helps.