Question

The hand shook violently. Is violently a adjective or adverb?

Answer 1

Violently is an adverb. When there is an -ly at the end of the word, it will almost always be an adverb.

Answer 2

In this sentence, it's being used as an adverb. 
The word "violently" ends with an "ly" which makes it an adverb. 

Therefore, the answer would be: adverb.