(contactmusic.com ) - Rapper 50 Cent has been forced to quit pumping iron so he can tone down for a new movie role.The once-beefy hitmaker has trimmed down and grown an Afro hairstyle to play a New Orleans, Louisiana police officer in upcoming film Microwave Park.To make his weightloss more fun, 50 tells MTV.com he offered a challenge to his G-Unit posse - offering a cash prize to the associate who lost the most.Filming on the movie, which also stars Val Kilmer and Sharon Stone , starts next month (May08).