John Whitehead, R&B artist best known for the 1979 hit song “Ain’t No Stoppin’ Us Now,” was shot dead in Philadelphia on Wednesday. He was 55.Gene McFadden was Whitehead’s partner in the singing group McFadden & Whitehead. The two men formed a group called the Epsilons in their youth and were discovered by Otis Redding, touring with the legendary performer in the 1960s, according to their Web site. The duo wrote several hit songs performed by others in the 1970s, including “Back Stabbers,” “For the Love of Money,” “I’ll Always Love My Mamma,” “Bad Luck,” “Wake Up Everybody,” “Where Are All My Friends,” “The More I Want” and “Cold, Cold World.” “Ain’t No Stoppin’ Us Now” went to No. 1 on the R&B chart and reached No. 13 on the pop chart. The song became an unofficial anthem for the Phillies as they charged to a World Series championship in 1980 and the Eagles as they reached the Super Bowl in 1981. Survivors include a daughter.