May one work on Tisha B’Av?
It is permitted to work after halachic noon (chatzos). However, one should try to avoid such work and dealings that cause a person to be distracted from mourning; Chazal state that one who engages in work on Tisha Be’Av at the expense of being distracted from mourning will not see any blessing from his work.
Sources: The prohibition on working on Tisha B’Av depends on custom. Rema writes that the custom is to refrain from work before chatzos (halachic noon), but not after chatzos (Orach Chaim 554:22). Yet, somebody who is pious (yarei shamayim) should refrain from working altogether (Chayei Adam 135:18; Kitzur Shulchan Aruch 124:15). When a loss is involved, it is permitted to work (as on Chol Hamo’ed; Orach Chaim 554:23), but Chazal write that one does not see blessing from work done on Tisha B’Av (554:24).