Therefore, by setting θj = π in (11), we note that the first particle will fall to the ground
in a time tmin =
2H
g
+
V1
g
2
− V1
g . On the other hand, by setting θj = 0 in (11), we may see
that the last particle reaches the ground in a time tmax =
2H
g
+
V1
g
2
+ V1
g . We would now
like to prove that each group of particles Gj describes a circle on the ground with a variable
radius. In order to see this, let us consider equations (10a) and (10c) for τ = τ j and write