  We consider a static spherically symmetric thin shell wormhole collides with
another thin shell consisting of ordinary matter. By employing the geometrical
constraint, which leads to the conservation of energy and momentum, we show
that the state after the collision can be solved from the initial data. In the
low speed approximation, the solutions are rather simple. The shell may either
bounce back or pass through the wormhole. In either case, the wormhole shrinks
right after the collision. In the "bouncing" case, a surprising result is that
the radial speeds before and after the collision satisfy an addition law, which
is independent of the masses of the wormhole and the shell. Once the shell
passes through the wormhole, we find that the shell always expands. However,
the expansion rate is the same as its collapsing rate right before the
collision. Finally, we find out the solution for the shell moving together with
the wormhole.
