It more probably prevents implantation in the uterus. Conception can't be stopped if sperm is allowed through the cervix (except for the pill, which prevents follicles from ripening to eggs).
No, wrong. See post #165, and also Mechanisms of action of mifepristone and levonorgestrel when used for emergency contraception, and Post-coital administration of levonorgestrel does not interfere with post-fertilization events in the new-world monkey Cebus apella, and also here
I wrote in a later post that I stood corrected by your #165. Luck may be close to 50% in the workings of the progesterone hot of the morning after pill.