I just looked up impetus on dictionary.com to verify that the plural is impetuses. [It is.] For a quote that used the word in a sentence, the dictionary provided this shining gem by the horrendous bilgewhacker D.H. Lawrence:
"While the white man keeps the impetus of his own proud, onward march, the dark races will yield and serve, perforce. But let the white man once have a misgiving about his own leadership, and the dark races will at once attack him, to pull him down into the old gulfs."
Apparently this comes from a 1920s novel by Lawrence entitled The Plumed Serpent. Stupid condescending crap from the main character Kate.
Maybe the dictionary.com quote generator should exclude bigoted tripe, huh?
P.S. The title of this entry comes from Yo, Is this Racist?, a hilarious [and ableist] Q&A blog.