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Homework Help: Terminal Velocity

  1. Aug 5, 2015 #1
    1. The problem statement, all variables and given/known data
    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
    2. Relevant equations
    terminal speed = sqrt[(2mg)/(Cpa)]
    volume*density = mass

    3. 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.
  2. jcsd
  3. Aug 5, 2015 #2
    Lots of numbers to chase, but 1.6 m/s makes no sense.
  4. Aug 6, 2015 #3

    rude man

    User Avatar
    Homework Helper
    Gold Member

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