In question 1.2, why the answer is strong nuclear?
The weak force only concerns leptons, and also only concerns decay. The given particle equation shows an interaction between a pion and a proton, not a decay. So it can't be the weak force.
so in weak interaction, only one particle can be on the left side of the equation? What I originally thought is that pion decayed into Kaon. I know it is wrong but i dont know the reason.