Internal resistance (( r )) was a common stumbling block. Students would calculate ( V = IR ) using the battery’s EMF (( \mathcalE )) instead of the terminal voltage ( V_terminal = \mathcalE - Ir ).
There is a general consensus among physics educators that the older free-response questions were often more mathematically demanding than some modern equivalents (specifically compared to the early years of AP Physics 1). Working through the 1984 AP Physics B Free Response builds "mental stamina." If you can solve a 1984 E&M problem, you are likely well-prepared for the algebraic rigors of current exams. 1984 ap physics b free response