Questions & Answers about كان انهيار الجسر مفاجئا.
The lesson is about Form VII verbal nouns. How does انهيار fit this pattern?
The word انهيار (collapse) follows the standard Form VII verbal noun pattern, which is انفعال (infi'āl). It comes from the verb انهار (to collapse). Even though the root is a bit irregular, you can see and hear the classic Form VII pattern clearly: it starts with the prefix انـ (in-) and places a long ـا (-ā-) right before the final letter.
Why doesn't انهيار have الـ (al-) attached to it, since the English translation says 'The collapse'?
انهيار is the first word in an idafa (a possessive phrase), specifically انهيار الجسر (the collapse of the bridge). A strict rule of the idafa is that the first word never takes الـ (al-), even when it translates with 'the' in English. It gets its definite 'the' meaning automatically from the second word, الجسر (the bridge).
Why does مفاجئا (sudden) end with an extra alif and two lines (fathatayn)?
That ending marks the accusative case. The verb كان (was) has a special grammatical rule: its subject (here, انهيار) takes the standard nominative case, but its predicate (the describing word, مفاجئا) must take the accusative case. The extra alif and two tick marks show this case change.
The verb كان (was) is masculine. Is it matching the gender of 'collapse' or 'bridge'?