Final answer:
The function modeling the radius of a circular ripple as a function of time is g(t) = 80t, with the ripple traveling outward at a constant speed of 80 cm/s.
Step-by-step explanation:
The function g(t) that models the radius of a circular ripple as a function of time when a stone is dropped in a lake can be determined by the constant speed at which the ripple travels outward. Since the ripple travels at 80 cm/s, the radius of the ripple increases linearly with time. Therefore, the function is g(t) = 80t, where t is the time in seconds after the stone is dropped.