  In this paper, we consider the initial value problem for nonlinear wave
equation with weighted nonlinear terms in one space dimension. Kubo & Osaka &
Yazici(2013) studied global solvability of the problem under different
conditions on the nonlinearity and initial data, together with an upper bound
of the lifespan for the problem. The aim of this paper is to improve the upper
bound of the lifespan and to derive its lower bound which shows the optimality
of our new upper bound.
