4. Trilobites are animals that lived during the Paleozoic era. They populated all parts of the ocean showed consistent evolution over time and left behind fossils that are large
enough to be studied without a microscope. All of these characteristics make trilobites
the ideal
a. Trace fossil
b. Keystone species
c. Index fossil
d. Reference point
dnreserve the remains of dead

Two steel balls, each of mass m, are welded to a light rod of length l and negligible mass and are initially at rest on a smooth horizontal surface. a horizontal force of magnitude f is suddenly applied to the rod as shown. determine (a) the instantaneous acceleration a of the mass center g and (b) the corresponding rate at which the angular velocity of the assembly about g is changing with time.