Abstract. -We present an exact derivation of the survival probability of a randomly accelerated particle subject to partial absorption at the origin. We determine the persistence exponent and the amplitude associated to the decay of the survival probability at large times. For the problem of inelastic reflection at the origin, with coefficient of restitution r, we give a new derivation of the condition for inelastic collapse, r < rc = e −π/ √ 3 , and determine the persistence exponent exactly. Consider a randomly accelerated particle, obeying the stochastic equation of motionwhere η t is Gaussian white noise with zero average, η t = 0, and correlator η t η t ′ = δ(t − t ′ ). This is the original Langevin equation with no damping force. The joint random variables (x t , v t ) evolve in time aswith initial conditions (x 0 , v 0 ). Thereforewhere W t is the integral of the noise, or Brownian motion, hence the process x t is usually referred to as the integral of Brownian motion. The statistics of the times of first passage by the origin, and of related quantities, for a particle obeying (1), has been the subject of a long series of works, and is by now well understood [1][2][3][4][5].More recently, a number of studies have been devoted to survival problems for a randomly accelerated particle, with particular choices of the boundary conditions at the origin, motivated by situations of physical interest.c EDP Sciences