Atom A (mass m) moves to the right at 200m⋅s−1 toward identical atom B, which is at rest (both atoms lie along the same line as a fixed, perfectly rigid wall located to the right of atom B). The sequence is as follows:
1. Atom A collides elastically and head-on with atom B.
2. Atom B travels to the right and collides elastically with the wall, reversing its velocity without loss of speed.
3. Atom B (now moving left) collides elastically and head-on with the stationary atom A.
After this entire sequence, what is the speed and direction of atom A?
a) 100m⋅s−1 to the left
b) 200m⋅s−1 to the left
c) 0m⋅s−1 (at rest)
d) 200m⋅s−1 to the right