  Chondrules are one of the most primitive elements that can serve as a
fundamental clue as to the origin of our Solar system. We investigate a
formation scenario of chondrules that involves planetesimal collisions and the
resultant impact jetting. Planetesimal collisions are the main agent to
regulate planetary accretion that corresponds to the formation of terrestrial
planets and cores of gas giants. The key component of this scenario is that
ejected materials can melt when the impact velocity between colliding
planetesimals exceeds about 2.5 km s$^{-1}$. The previous simulations show that
the process is efficient enough to reproduce the primordial abundance of
chondrules. We examine this scenario carefully by performing semi-analytical
calculations that are developed based on the results of direct $N$-body
simulations. As found by the previous work, we confirm that planetesimal
collisions that occur during planetary accretion can play an important role in
forming chondrules. This arises because protoplanet-planetesimal collisions can
achieve the impact velocity of about 2.5 km s$^{-1}$ or higher, as protoplanets
approach the isolation mass ($M_{p,iso}$). Assuming that the ejected mass is a
fraction ($F_{ch}$) of colliding planetesimals' mass, we show that the
resultant abundance of chondrules is formulated well by $F_{ch}M_{p,iso}$, as
long as the formation of protoplanets is completed within a given disk
lifetime. We perform a parameter study and examine how the abundance of
chondrules and their formation timing change. We find that the impact jetting
scenario generally works reasonably well for a certain range of parameters,
while more dedicated work would be needed to include other physical processes
that are neglected in this work and to examine their effects on chondrule
formation.
