Calculating Drag (having circular reference problems)

[josiahseto]

Homework Statement

I don't know if it's possible but I am doing a physics EEI on drag.
I know to find drag you need instantaneous velocity which can be found through (change in x/ change in t) but i cannot find displacement unless i find velocity :S..

Homework Equations

d = 0.5 x p x (V^2) x Cd x A
im taking p = 1.2
Cd = 1.05 (for square shape)
A = 0.0225 sq meters

The Attempt at a Solution

I have dropped a square open sided cube 15cm x 15cm through a vertical distance of 2.5m (u = 0m/s) and it took an average of 2.33s

 

[josiahseto]

also, its mass is 0.0029 kg
so w = 0.02842N

therefore at terminal velocity point drag = 0.02842N (thats if it does reach TV)

therefore at that point acceleration = 0

so.. we have

u = 0m/s

v = 1.41m/s (calculated through Fd = Fg)

and a = 0m/s at TV point

 

[rock.freak667]

the velocity can be found using v²=u²-2gy

 

[josiahseto]

v^2 = 0^2 - 2 x 9.8 x 2.5
V^2 = -49
v = sqrt -49 = impossible?

 

[rock.freak667]

v^2 = 0^2 - 2 x 9.8 x 2.5
V^2 = -49
v = sqrt -49 = impossible?

Sorry, down is positive, so it would be v^2=0^2+2*9.81*2.5.