Question

is the altitude of a triangle (sometimes,always,never) the perpendicular bisector?

Answer 1

An altitude is a line segment that connects one vertex of a triangle to the opposite side (or the line containing it), such that the two lines are perpendicular.
This means that it will always be a perpendicular line, so the only other criterion to check is that it bisects the opposite side as well. Note these are all possible altitudes:

It can, in some specific cases, bisect the opposite side. But it does not always bisect the opposite side.