Rychlost auta je vysoká.

Because auta is the genitive singular form of auto.

In Rychlost auta, the structure is literally speed of the car. Czech often expresses of X by putting X into the genitive case.

• auto = car
• auta = of the car

So:

• rychlost auta = the speed of the car

This is a very common pattern in Czech:

• barva domu = the color of the house
• jméno člověka = the name of the person

Because it agrees with rychlost, which is a feminine noun.

In Czech, adjectives usually agree with the noun they describe in:

• gender
• number
• case

Here, the subject is rychlost (speed), and rychlost is feminine singular. So the adjective must also be feminine singular:

• masculine: vysoký
• feminine: vysoká
• neuter: vysoké

So:

• Rychlost je vysoká.

Even though auta is also in the sentence, vysoká does not agree with auta. It agrees with rychlost.

Yes. In this sentence, vysoká is in the nominative singular feminine form.

That is because it is a predicate adjective after the verb být (to be), and in Czech predicate adjectives are normally in the nominative:

• Dům je velký. = The house is big.
• Voda je studená. = The water is cold.
• Rychlost auta je vysoká. = The speed of the car is high.

So both the subject rychlost and the predicate adjective vysoká are nominative feminine singular.

In standard Czech, je is normally used here.

• Rychlost auta je vysoká. = correct standard sentence

Czech does sometimes omit forms of být in special styles, such as:

• headlines
• notes
• very informal speech
• poetry

But for normal standard sentences, you should keep je.

So as a learner, it is safest to say:

• Rychlost auta je vysoká.

Because Czech has no articles like English a / an / the.

So Czech simply says:

• rychlost auta

and the exact English translation depends on context:

• the speed of the car
• a car’s speed
• car speed

Very often, the context tells you whether something is definite or indefinite.

If you want to make it more specific, Czech can use demonstratives like:

• to auto = that / the car
• tohoto auta = of this car
• toho auta = of that/the car

But there is no separate word that works exactly like English the.

The word order is fairly flexible, but Rychlost auta je vysoká is the most neutral and natural order.

Czech word order often changes for:

• emphasis
• topic and focus
• style

Possible alternatives may sound natural in certain contexts, for example:

• Vysoká je rychlost auta.
• Rychlost toho auta je vysoká.

But the basic learner-friendly order is:

• Rychlost auta je vysoká.

That puts the subject first, then the verb, then the predicate adjective, which is easy and neutral.

Yes, but that is not the same kind of structure.

• Rychlost auta je vysoká. = a full sentence: The speed of the car is high.
• vysoká rychlost auta = a noun phrase: the high speed of the car

So:

• Rychlost auta je vysoká. has a verb and makes a complete statement.
• Vysoká rychlost auta is just a phrase, not a complete sentence by itself.

It is simply the normal Czech collocation.

Czech commonly uses vysoký / vysoká / vysoké with things like:

• rychlost = speed
• cena = price
• teplota = temperature
• kvalita = quality

So vysoká rychlost is the normal way to say high speed.

You might sometimes hear or see velká rychlost, and it can be understandable, but vysoká rychlost is the more standard and idiomatic choice.

You often have to learn the gender with the noun, but there are some clues.

Rychlost ends in -ost, and many Czech nouns ending in -ost are feminine:

• radost = joy
• možnost = possibility
• rychlost = speed

That is why you get:

• ta rychlost
• rychlost je vysoká

So although noun endings are not a perfect rule, -ost is a strong clue for feminine nouns.

Approximately like RIKH-lost, with the stress on the first syllable:

• RYCH-lost

A few pronunciation notes:

• Czech stress is almost always on the first syllable
• ch is one sound, like the ch in Scottish loch or German Bach
• r is rolled or tapped
• y is a short vowel, not like English eye

And:

• auta is roughly OW-ta, where au sounds like English ow in cow

Yes, in form alone it can.

auta can be:

• genitive singular of auto = of the car
• nominative/accusative plural = cars
• in some contexts other plural-related forms can be involved as well

But in this sentence, the grammar makes the meaning clear:

• Rychlost auta most naturally means the speed of the car

That is because after a noun like rychlost, Czech commonly uses the genitive to mean of something.

So here, learners should understand auta as genitive singular.

Yes, but Czech usually expresses that differently from English.

A natural version would be:

• Jeho rychlost je vysoká. = Its / his speed is high.

If you specifically mean the speed of the car, Czech often still prefers the noun:

• Rychlost auta je vysoká.

Czech does not use possessive pronouns exactly the same way English does in every situation, so the noun phrase with genitive is often the most straightforward choice.