The High-Luminosity LHC aims to provide a total integrated luminosity of 3000/fb from proton-proton collisions at sqrt(s) = 14 TeV over the course of ~10 years, reaching instantaneous luminosities of up to L = 7.5 x 10^34/cm^2/s, corresponding to an average of 200 inelastic p-p collisions per bunch crossing (mu = 200). Fast simulation studies have been carried out to evaluate the prospects of various benchmark physics analyses to be performed using the upgraded ATLAS detector with the full HL-LHC dataset. The performance of the upgrade has been estimated in full simulation studies, assuming expected HL-LHC conditions. This talk will focus on the results of physics prospects studies for benchmark analyses involving in particular boosted hadronic objects (e.g. ttbar resonances, HH resonances (HH->bbbb) and dijet resonances), and on results of Jet/EtMiss studies of jet performance and pileup mitigation techniques that will be critical in HL-LHC analyses.