  We employ a three-dimensional (3D) reconstruction technique, for the first
time to study the kinematics of six coronal mass ejections (CMEs), using images
obtained from the COR1 and COR2 coronagraphs on board the twin STEREO
spacecraft, as also the eruptive prominences (EPs) associated with three of
them using images from the Extreme UltraViolet Imager (EUVI). A feature in the
EPs and leading edges (LEs) of all the CMEs was identified and tracked in
images from the two spacecraft, and a stereoscopic reconstruction technique was
used to determine the 3D coordinates of these features. True velocity and
acceleration were determined from the temporal evolution of the true height of
the CME features. Our study of kinematics of the CMEs in 3D reveals that the
CME leading edge undergoes maximum acceleration typically below 2R$_\{odot}$.
The acceleration profiles of CMEs associated with flares and prominences
exhibit different behaviour. While the CMEs not associated with prominences
show a bimodal acceleration profile, those associated with prominences do not.
Two of the three associated prominences in the study show a high and rising
value of acceleration up to a distance of almost 4R$_\{odot}$ but acceleration
of the corresponding CME LE does not show the same behaviour, suggesting that
the two may not be always driven by the same mechanism. One of the CMEs,
although associated with a C-class flare showed unusually high acceleration of
over 1500 m s$^{-2}$. Our results therefore suggest that only the
flare-associated CMEs undergo residual acceleration, which indicates that the
flux injection theoretical model holds good for the flare-associated CMEs, but
a different mechanism should be considered for EP-associated CMEs.
