Terminal Velocity of Cube: 1.6 m/s

[Dalip Saini]

Homework Statement

cube has a drag coefficient of 0.90. What would the terminal velocity of this cube be, 1.0 cm on a side in air (ρ = 1.2 kg/m3)? Take the density of this cube to be 1.6 x 103 kg/m3.

• 
  
  A
  
  68 m/s
• 
  
  B
  
  1.6 m/s
• 
  
  C
  
  5.6 m/s
• 
  
  D
  
  20 m/s
• 
  
  E
  
  360 m/s

Correct answer is 1.6 m/s

Homework Equations

terminal speed = sqrt[(2mg)/(Cpa)]
volume*density = mass

The Attempt at a Solution

(0.01 m)^3(1.6E3 kg/m^3) = 1.6E-3 kg
terminal speed = sqrt [((2(1.6E-3)(9.8))/((0.9)(1.2)(0.01)^2)] = 17.04 m/s but the answer is 1.6 m/s. I don't understand what I did wrong.

 

[Dr. Courtney]

Lots of numbers to chase, but 1.6 m/s makes no sense.

 

[rude man]

Hint: the given answer isn't always right!
(I got same as yours).