1. Not finding help here? Sign up for a free 30min 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!

Time on watch dependent on air temperature?

  1. Mar 30, 2010 #1
    1. The problem statement, all variables and given/known data
    Can anyone give me a hand on how to start this? I would attempt a solution but I've tried over and over and can't seem to get anywhere.

    A man sets his watch at noon by the sound of a factory whistle 3 miles away. If the temperature of the air is 20-degrees C, how many seconds slow will his watch be by the time at the factory?


    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Mar 30, 2010 #2

    DaveC426913

    User Avatar
    Gold Member

    How fast does sound travel through air at 20C?
     
  4. Apr 1, 2010 #3

    Still a little lost here:

    In general, at 68 F (20 C) sound travels at 1130 ft/sec (344.4 m/sec.)
    3 miles = 15 840 feet
    3 miles = 4 828.032 meters

    but not sure how to put it together in equation format?
     
  5. Apr 1, 2010 #4

    DaveC426913

    User Avatar
    Gold Member

    Really?

    You've got a velocity and a distance; you're being asked to solve for time.

    You say you're tried over and over. Show your attempts.
     
  6. Apr 1, 2010 #5
    T=V/D =
    T=15840 ft/ 1130ft/s = 14.018 seconds.
     
  7. Apr 1, 2010 #6

    DaveC426913

    User Avatar
    Gold Member

    Does that sound about right? What does your intuition tell you? Think of thunder & lightning.
     
  8. Apr 1, 2010 #7
    I did find something that used c = d / Δ t - where c was speed of sound so
    Δ t = d / c = 15,840/344.4 = 46 seconds but that seems too long a delay for three miles no?

    As far as thunder and lightning, lightning strikes first b/c it travels faster in air than sound. The speed of a sound wave in air depends upon the properties of the air, namely the temperature and the pressure so it makes sense for
    Time=distance/speed =
    Time=15,840 ft/1130 ft/sec.
    14.018 sec

    but i'm still second-guessing it.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Time on watch dependent on air temperature?
  1. Air Temperature (Replies: 10)

Loading...