Answer:
the diferencial equation is
dv(t)/dt + (k/m) v(t) + g = 0
Explanation:
the differential equation for determining the instantaneous speed can be found from Newton's second law:
F= m*a
F drag + F gravity = m*a
(-k*v) + (-m*g) = m*a , where g is acceleration due to gravitational force
since a = dv/dt and dividing both sides by m
dv(t)/dt = -g- k/m v(t)
or
dv(t)/dt + (k/m) v(t) + g = 0