I'm puzzled by the use of the preposition у with the verb спросить:
Я спрошу у мамы смогу ли взять машину
In this example, the preposition is used. But:
Журналист спросил президента о его планах на будущее
In this example, the preposition is not used. Is the meaning the same in these two sentences? As far as I know, in both instances the meaning is "to ask someone (about) something".
Both forms "спросить у кого-то" and "спросить кого-то" are equally valid - the difference is very, very subtle and you can find a lot of answers in internet that are nothing but wrong. It wouldn't be oversimplification to say - those form a virtually equivalent.
The only difference I'm aware of - and it's only a statistical observation, I can not provide any grammar rule or other evidence - when it comes to inanimate objects, the "у"-form is more likely.
For instance, there's a famous song which contains following lyrics: "Я спросил у ясеня, где моя любимая". One can not say "я спросил ясень" but "у ясеня" sounds more natural. I'm leaving behind the brackets here the fact that it's strange to communicate with inanimate objects but I can imagine following phrases:
They both have the same meaning but require different cases genitive and accusative. Besides,I feel that prepositional usage sounds more colloquial.
I think the difference between спросить меня vs спросить у меня is very similar to the difference between give me and give to me.
When there is a direct object, or even another indirect object between the verb спросить and the addressee of the question (for example 'спросить разрешения у меня'), then you have to use the preposition у. But even if there is no word in between, the language allows to use the preposition у just by inertia. The meaning is the same, maybe just the speaker emphasizes to whom the question is addressed (спросить у президента). So even when you do not hear well or do not listen attentively, you still will understand :-)
