It has been shown that the thermal photon and the lepton pair spectra can be used to estimate the radial velocity of different phases of the matter formed in nuclear collisions at ultrarelativistic energies. We observe a nonmonotonic variation of the flow velocity with invariant mass of the lepton pair, which is indicative of two different thermal dilepton sources at early and late stages of the dynamically evolving system. We also show that the study of radial velocity through electromagnetic probes may shed light on the nature of the phase transition from hadrons to a quark-gluon plasma.