Is it obligatory for the worshipper (ma'mum) to listen attentively to the imam's recitation in a silent prayer if he hears it, or should he recite Al-Fatiha, and should he say "Ameen" aloud if he is listening attentively to the imam?

In congregational prayers, it is prescribed to recite aloud (jahr) in Fajr, Maghrib, Isha, and Jumu'ah prayers, and silently (sirr) in Dhuhr and Asr prayers. The Imam recites aloud in the audible prayers, and the follower listens attentively and recites Al-Fatihah. As for the silent prayers, the follower recites Al-Fatihah and a surah. It is permissible for the Imam to sometimes allow the followers to hear a verse in a silent prayer, but this does not make the prayer cease to be silent. This audible recitation is not intended for its own sake, but rather to let people know that he is reciting or to alert them. If the Imam intentionally recites aloud in a silent prayer, contrary to the Sunnah, he should be prohibited from doing so, as it distracts the worshippers.