TITLE: examples of additive categories which have morphism that has no kernel and morphism has no cokernels.
QUESTION [6 upvotes]: can you tell me examples of additive categories which have morphism that has no kernel and morphism has no cokernels.
if you tell me reference which provide this kind of examples it will be great.thanks.

REPLY [4 votes]: A typical example is the category of vector bundles on a (non-pathological) topological space.
The corresponding algebraic example is the category of finitely generated projective modules over some (non-pathological) commutative ring. 
Notice: If $K \to P$ is a kernel of $P \to Q$ in the category of f.g. proj. $R$-modules, then this is also the kernel in the category of all abelian groups. The reason is that $\hom(R,-)$ is left exact and that it identifies with thr forgetful functor. Therefore, it suffices to find an example of a map between f.g. projective modules whose "usual" kernel (i.e. the one in the category of abelian groups) is not projective. Unfortunately, there is no such argument for cokernels, which will be more complicated.