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!

At how many rpms will a blade tip break the sound barrier

  1. Sep 7, 2014 #1
    1. The problem statement, all variables and given/known data
    The windmill is 400 feet tall and each of it's three blades are 130 feet long. At how many rpms will a blade tip break the sound barrier? Speed of sound: 1125ft/sec


    2. Relevant equations
    Linear speed: v = rω
    Angular speed: ω = Θ/Time


    3. The attempt at a solution
    1125ft/sec = 130ft(ω)
    ω = 1125ft/sec * 1rad/130ft ≈ 9
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Sep 7, 2014 #2

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    What are the units of the number 9? Are they RPMs like what was requested in the OP?

    Hint: RPM usually means 'revolutions per minute'.
     
  4. Sep 7, 2014 #3
    Sorry, the 9 is in radians per second, but the problem is I get stuck there. I know I need the linear speed...but I don't how to go about doing that in this situation.
     
  5. Sep 7, 2014 #4
    You have already solved this problem! You are looking for an answer in rpm's. You have a solution in radians per second. There is only a conversion to do from here.
     
  6. Sep 8, 2014 #5

    Redbelly98

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    You already have the linear speed, 1125 ft/sec, as used in your originally posted attempt at a solution.
     
  7. Sep 8, 2014 #6
    Thanks, I got it figured out, I don't know why this confused me so much...
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: At how many rpms will a blade tip break the sound barrier
  1. How many gas molecules (Replies: 4)

  2. How many nodal lines? (Replies: 1)

Loading...