Acceleration in free fall w/ air drag given velocity and mass

[elsternj]

Homework Statement

On September 8, 2004, the Genesis spacecraft crashed in the Utah desert because its parachute did not open. The 210-kg capsule hit the ground at 311 km/h and penetrated the soil to a depth of 81.0cm . Assuming it to be constant, what was its acceleration (in m/s² ) during the crash?

Homework Equations

F=ma
f=Dv²

The Attempt at a Solution

m=210kg
g=9.8m/s
w=2058N
v_y=86.4m/s

F_y=w-f=ma
F_y=mg-Dv²=ma
=2058-D(86.4)²=210a

Now I have D and a as unknowns. Not sure where I am going wrong here. I have equations with D in them for terminal speed but i am assuming this doesn't reach terminal speed because then a would be equal to 0 would it not? and 0 is not the right answer. those equations would then have v and D as unknowns.

 

[PhanthomJay]

This is not a problem about terminal velocity or wheteher the craft is still accelerating while it is in the air and before it hits the ground. Rather, the deceleration asked for is during the impact time when the ship is in contact with the ground over 81 cm.. You don't need to calculate any forces...just the acceleration using one of the kinematic equations of motion.