Udarac je jak.

Because je is a clitic in Croatian. Clitics are short unstressed words that usually go in the second position of the sentence or clause.

So in Udarac je jak, the first element is Udarac, and je comes right after it.

This is very normal in Croatian:

• Udarac je jak.
• On je jak.
• Ovaj udarac je jak.

You usually cannot place je freely wherever you want.

Je is the 3rd person singular present tense of biti (to be).

So it corresponds to is in English.

• ja sam = I am
• ti si = you are
• on/ona/ono je = he/she/it is

In Udarac je jak, je links the subject (udarac) with the adjective (jak), just like is in English.

Because the adjective must agree with the noun in gender, number, and case.

Udarac is:

• masculine
• singular
• nominative

So the adjective must also be:

• masculine
• singular
• nominative

That gives jak.

Compare:

• udarac je jak = the blow is strong
• ruka je jaka = the hand is strong
• vino je jako = the wine is strong

It is in the nominative singular, because it is the subject of the sentence.

The basic dictionary form is also udarac, so this sentence uses the noun in its base form.

In a simple sentence like this:

• Udarac = subject
• je = verb
• jak = predicate adjective

Croatian does not use articles like English a/an/the.

So udarac can mean:

• a blow
• the blow

Which one is meant depends on the context.

That is very normal in Croatian. You do not need to add a separate word for the or a.

Yes, jak is natural and means strong, powerful, or sometimes intense, depending on context.

With udarac, jak is perfectly normal:

• jak udarac = a strong blow
• Udarac je jak. = the blow is strong

You may also encounter snažan, which can also mean strong/powerful:

• Udarac je snažan.

Both are possible, though jak is very common and straightforward.

Yes, Croatian word order is fairly flexible, but not completely free.

The neutral order here is:

• Udarac je jak.

You might also hear:

• Jak je udarac. — puts more focus on jak
• Udarac je stvarno jak. — adds really
• Taj udarac je jak. — that blow is strong

But remember: je still tends to stay in second position.

So even when word order changes, the placement of clitics is still important.

It is an adjective.

It describes the noun udarac, even though it comes after the verb je.

In English, adjectives can also appear after to be:

• The blow is strong.

Croatian works the same way here:

• Udarac je jak.

If it were an adverb, it would describe a verb, not a noun.

In standard Croatian, yes, if you are making a normal present-tense sentence like this.

So:

• Udarac je jak. = correct

Without je:

• Udarac jak.

This is generally not standard as a full normal sentence, though you might see omission of je in:

• headlines
• notes
• poetry
• very informal speech

For learners, it is best to keep je.

A simple approximation is:

U-dah-rats

More carefully:

• u like oo in boot
• d as in dog
• a like a in father
• r is a rolled or tapped r
• c in Croatian is pronounced like ts

So the ending -ac sounds roughly like -ats.

A simple pronunciation guide is:

U-dah-rats yeh yahk

Roughly:

• Udarac = U-dah-rats
• je = yeh
• jak = yahk

A few useful sound notes:

• j in Croatian is like English y in yes
• a is usually like a in father
• k is always clearly pronounced

So jak is not like English jack. It sounds more like yahk.