credible, demur, intensive, prevail, stalwart
Justin Timberlake will be starring as an American war hero in Stop Loss, an upcoming film about the war in Iraq. The movie's producers initially demurred to his playing the part, as they did not believe he would be credible in the role of a stalwart soldier. Justin prevailed upon them, and he plans to prepare for the role with intensive exercise.
demur - (verb) to oppose [This word is usually used with the prepositions "to" or "at."]
credible - (adjective) able to be believed; convincing
stalwart - (adjective) having great strength; displaying little or no fear
prevail - (verb) to persuade [The usage of this word in this context is usually associated with the prepositions "upon" or "on."]; to triumph; to be predominant; to win out
intensive - (adjective) highly concentrated; tending to give force or strengthen