posted by Jan .
You encounter a moving walkway that is 97 m long and has a speed of 2.0 m/s relative to the ground.
How long would it take you to cover the 97 m length of the walkway if, once you get on the walkway, you immediately turn around and start walking in the opposite direction with a speed of 1.5 m/s relative to the walkway?
Your forward speed relative to the building will be 2.0 - 1.5 = 0.5 m/s.
Divide 97 m by that speed for the required time, in seconds.