Today, Duolingo taught me that it's Какая глубина этого озера?, but Какая ширина у этой улицы?. My questions are

  1. Is that a case of binary grammaticality? I. e., would Какая глубина у этого озера? or Какая ширина этой улицы? be ungrammatical or unusual?
  2. If yes, is either of these cases an exception? That is, do/don't you usually use у with physical quantities? If no, is there a rule or can you give me a table relating common quantities to their use of у?
  3. What about more "technical" quantities, such as density, potential, or flux?

2 Answers 2

  1. No, either way is correct (in either case), and I even struggle to say which one is more common.
  2. I'd say that usually we don't use y with physical quantities (or qualities); plain Genitive is the 'default' way applicable to everything. Площадь кухни, плотность свинца, возраст дочери, напряжение обмотки, цвет стены. So the basic rule is simple: if in doubt, don't use y.
  3. As above, generally without y. Having the preposition makes the phrase slightly less formal (or so it feels to me), and technical/formal writing avoids it.
  • 3
    Some orderings of words do require the preposition. Какая ёмкость [у] этой цистерны? Какая у этой цистерны ёмкость? Dec 23, 2019 at 2:40
  1. Yes, in combination with the question word какой(-ая) in your examples, omitting the preposition у sounds a bit unusual if not awkward. Probably, it's because the question is about assigning a value to an object (like, what depth/width value it has). You don't need a preposition with another question word, каков(а), since the question would focus on the value only (how much its width value is):

Какова ширина этой улицы?
Какова глубина этого озера?

  1. A possible context with the question word какая but without need for у (as above, value is in focus):

Какая глубина этого озера сделала бы его судоходным?
Какая ширина этой улицы могла бы исключить пробки?

  1. In formal cases (scientific or engineering writings) preposition у is avoided (except when it means near), so the question word is selected so that it provides focusing on value:

Какова скорость света в полипропилене?
Какая температура плавления этого сплава обеспечит заданные характеристики объекта?

  • 1
    Also compare with: "Какой ширины эта улица?" Dec 22, 2019 at 19:22

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