(See attached file for full problem description with diagrams)
Two identical pulses are moving in opposite directions along a stretched string that has one fixed end and the other movable, as shown in the figure.
Above each pulse a green arrow indicates the direction of motion of the pulse.
The two pulses reflect off the boundaries of the string, and at some later time, they pass through the middle of the string and interfere.
Below are six different sequences of snapshots taken as the two pulses meet in the middle of the string. Time increases from top to bottom in each sequence. Which sequence correctly represents the displacement of the string as the pulses interfere?