Translation:A dress is getting torn
pasuka (to be torn open) is the stative passive form of pasua (to tear open), just like pendeka (to be liked) is the stative penda form of penda (to like). it's a brand new verb derived from the original.
keep in mind stative passive in swahili is different than "normal" passive (dynamic passive), in english the passive voice as in "the dog is fed" can have two meanings:
- The dog is fed (twice a day).
- The dog is fed (so we can leave now).
in swahili these are two different grammatical constructions, and the stative passive refers exclusively to the the second definition.
meanwhile the "-iwa" ending indicates the dynamic passive derivation, again another separate verb that is just derived from pasua. "anapasuliwa" refers to the first meaning of "the dog is fed".
Without "ka", this would mean that the dress is tearing something else, not that it is being torn. I'm not sure if it's passive or what the exact function is, but that is the difference between kupasua and kupasuka. As for li-, it is the prefix for Ji class nouns. Every noun class has its own prefixes.
this is the stative passive, not the dynamic passive (-wa), see: https://en.wiktionary.org/wiki/Appendix:Swahili_verbal_derivation#Stative