determined and stubborn when trying to solve or complete something

determined, persistent

an animal that is the young of a horse and a donkey; a slipper without a heel

stubborn

concerned with useful results, the possibility of actually being done (and not theory or principles)

sensible

demanding and enforcing obedience; severe; strict; the back end (of a ship or boat)

serious, authoritarian

(of a person) having a strong, determined will; difficult to deal

obstinate, unyielding

designed for use rather than beauty

practical