Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
flop [flɔp] n (failure) прова́л
vi (fail) прова́ливаться (провали́ться*perf) (fall, into chair, onto floor etc) шлёпаться (шлёпнуться perf)
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.