what's the difference between in urbem and ad urbem?
in urbem is more 'into the city' (going inside)
ad urbem is more 'towards the city' (movement towards)
How does one know which noun ending goes with which preposition?
With most prepositions, you use the accusative, but with a few prepositions, seen below, you use the ablative
In urbem is accusative to mean "into the city",
In urbe is dative to mean "in the city",
Is that right?
urbe is ablative. in urbe specifies the location.