Free Falling Pebble

(a) What is the speed of a pebble 4 secs after it is dropped?
(b) What is the average speed during the 4 secs?
(c) At what instant does the pebble actually posssess this average speed?

The string: S7P5A51 (physical change - speed).
{mi} = {pebble, dropper, air}
Si = air containing pebble, space containing dropper
Independent Pj Problem (IPP): air containership,
Dependent Pj Problems (DPP): identity (of dropper), force (of dropper),
Pj Problem of Interest (PPI) is change (speed, velocity, acceleration,instantaneous time and duration are change problems).
The math:

1(a) The speed v, of a free falling object on earth where the acceleration due to gravity is constant at 32 ft/sec2 = 32t (where t is time in secs).
So at t = 4secs, the speed v = 32 x 4 = 128ft/sec.
(b) Distance d, = 16t2.
So, average speed = (16 x 16)/4 = 256/4 = 64 ft.
Average speed occured at t=2s; since v(2) = 64.
in general average speed occurs in t/2 secs.

Blessed are they that have not seen, and yet have believed. John 20:29