  Future experiments beyond the LHC era will measure high-momentum bosons ($W$,
$Z$, $H$) and top quarks with strongly collimated decay products that form
hadronic jets. This paper describes the studies of the performance of jet
substructure variables using the Geant4 simulation of a detector designed for
high energy $pp$ collisions at a 100 TeV collider. The two-prong jets from $Z'
\rightarrow WW$ and three-prong jets from $Z' \rightarrow t\bar{t}$ are
compared with the background from light quark jets, assuming $Z'$ masses in the
range 5 -- 40 TeV. Our results indicate that the performance of
jet-substructure reconstruction improves with reducing transverse cell sizes of
a hadronic calorimeter from $\Delta \eta \times \Delta \phi = 0.087\times0.087$
to $0.022\times0.022$ in most cases.
