Parachute Problem (diff. eq's)

[rahidz2003]

"A skydiver weighs 160 pounds (including equipment, etc.). She jumps off the airplane at an altitude of 15000 ft, waits for 15 seconds, and then opens her parachute. Assume that the air resistance force is proportional to the falling velocity of the skydiver (with prop. constant being k=0.5 during free fall, and k=10 with the parachute open). Also assume that the initial falling velocity is zero."

The problem asks to find the differential equation for the velocity of the skydiver...I'm not sure at all how to start, any help? Thanks a bunch

 

[Gene]

If I'm remembering my physics it sounds as though she weighs w and you want
F=w-kv and
F=ma=m(dv/dt)=(w/g)(dv/dt) so
w-kv=(w/g)(dv/dt)
is the equation. I'm willing to be corrected though.