Falling Body with Air Resist

F_total = F_grav - F_air

ma = mg - kv where k units are kg/sec

mdv/dt = mg - kv

put into standard order:

mdv/dt + kv = mg

dv/dt + vk/m = g

find u = e^∫k/mdt = e^kt/m

multiply by u:

e^kt/mdv/dt + e^kt/mvk/m = ge^kt/m

d/ds(se^kt/m) = ge^kt/m