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We consider the background of a rotating axially symmetric black hole. Letparticle 0 decay to two fragments 1 and 2 in the direction parallel to that ofparticle 0. It is shown that if decay occurs inside the ergoregion, bothparticles 1 and 2 move in the same direction as particle 0. For the scenario,when decay happens in the turning point of all three particles, we find thecondition when angular momenta of both particles 1 and 2 have the same sign. Weelucidate the relation between the approach of Wald that imposes constraint onmaximum and minimum energies of fragments and our approach. In doing so, weexpress the results in terms of characteristics of particle 0 and all particlemasses. The conditions of the maximum efficiency depending on the relationbetween masses is discussed. We find an explicit expression for angular momentaof particles 1 and 2. We discuss also particle decay for static black holes,when the Penrose process is impossible. Because of the absence of theergoregion in the static case, scenarios of decay for static black holes cansignificantly differ from those in the rotating background.

General properties of the Penrose process with neutral particles in the equatorial plane