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 of a bobsled

  1. Apr 21, 2010 #1
    1. The problem statement, all variables and given/known data
    A bobsled has a frontal area of 0.86 m^2 and a coefficient of drag of 0.267. The air density is 1.043 kg/m^3. Total mass of the sled and the bobsled driver and pushers is 827 kg. Friction in the runners is negligible. The track slopes down at an angle of 0.078 radians. What will be the terminal speed (m/s)?
    m=827kg g=9.81m/s^2 p=1.043kg/m^3 Cd=0.267 A=0.86m^2

    2. Relevant equations
    Fg=mg
    Fd=.5pCdAv^2


    3. The attempt at a solution
    Fg=Fd but i do not get the right answer. Am I missing something is the angle just to tell you that it is going downhill?

    mg=.5pCdAv^2
    827*9.81=.5*1.043*0.267*0.86*v^2
    8112.87=.11974683v^2
    v^2=67750.1859548
    v=260.289
    He wants us to leave all decimals until the final answer which he wants rounded to 3 places.
     
  2. jcsd
  3. Apr 21, 2010 #2
    For something falling straight down you would have Fg = Fd at terminal velocity.

    For a sled on a slope Fg and Fd do not have the same direction. Only the component of Fg parallel to the slope is equal to the drag.
     
  4. Apr 22, 2010 #3
    So if i understand correctly Fg=mg sin 0.078rad. Thanks for your help!
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook