begin vs get cracking

begin and get cracking both are verbs.

Word	Noun	Adjective	Verb	Adverb
begin	No	No	Yes	No
get cracking	No	No	Yes	No

As verbs, get cracking is a hyponym of begin; that is, get cracking is a word with a more specific, narrower meaning than begin:

begin (verb)	get cracking (verb)
take the first step or steps in carrying out an action	start to be active
set in motion, cause to start
begin to speak or say
begin to speak, understand, read, and write a language
achieve or accomplish in the least degree, usually used in the negative
begin an event that is implied and limited by the nature or inherent function of the direct object
have a beginning, in a temporal, spatial, or evaluative sense
be the first item or point, constitute the beginning or start, come first in a series
have a beginning characterized in some specified way
have a beginning, of a temporal event