1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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).
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted