Question

For incomplete cancellation to occur, opposite pulses must have

equal amplitudes
different energies
equal pulses
equal displacements

it seems like none of these are quite right but would different energies be the closest.

Answer 1

It depends on what opposite pulses means. If they mean pulses moving in opposite directions, and opposite in amplitude, then ëqual amplitudes"is probably the better answer. Whomever wrote this question was either sloppy, or has a cursory understanding of wave mechanics.