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!

The speed of sound

  1. Apr 13, 2009 #1
    Please help!! trying to catch up with class! topic: the speed of sound

    1. The problem statement, all variables and given/known data

    Determine the depth of water if an echo using sonar returns in 870 ms and the speed of sound in water is 5300 km/h.

    2. Relevant equations

    distance= speed * time
    depth=distance/2

    3. The attempt at a solution
    time= 870s
    speed= 5300km/h

    --------
    i'm stuck at the part on converting ms to h. i think the

    the answer i got is 0.64km

    870ms= 0.00024167h
    distance = 5300*0.00024167 = 1.28
    depth= 1.28/2 = 0.64
     
    Last edited: Apr 13, 2009
  2. jcsd
  3. Apr 13, 2009 #2

    mukundpa

    User Avatar
    Homework Helper

    Will it take some time to come back?
     
  4. Apr 13, 2009 #3
    i really have no idea. i missed two months of physics and now struggling.

    i think it took 870 ms to return.
     
  5. Apr 13, 2009 #4

    mukundpa

    User Avatar
    Homework Helper

    ms means mili second and mili is 10^-3?
     
  6. Apr 13, 2009 #5

    mukundpa

    User Avatar
    Homework Helper

    All units must be in same system (SI).

    length in meter
    time in second
     
  7. Apr 13, 2009 #6

    mukundpa

    User Avatar
    Homework Helper

    is km/hour is SI unit of velocity?
     
  8. Apr 13, 2009 #7
    isn't it?

    does it matter?

    if we'redoing this by meter and second, then this is my attempt

    d= 5300000m/s *0.87 s = 4,611,000m
    depth= 4,611,000/2 = 2,305,500

    --------
     
  9. Apr 13, 2009 #8

    mukundpa

    User Avatar
    Homework Helper

    did you converted hour in sec?? it will be 5300*1000/3600 m/s
     
  10. Apr 13, 2009 #9
    i give up. i'm going to bed!

    good night! thanks for helping
     
  11. Apr 13, 2009 #10

    mukundpa

    User Avatar
    Homework Helper

    d = v*t = (5300*1000/3600) m/s*(870/1000) s =
     
  12. Apr 14, 2009 #11
    Your answer of .64km looks good to me (and seems like a reasonable depth). So this question seems to be mainly about unit conversions.
    Start with 870 ms . Now we know that ms means milliseconds, and that milli means 10^-3
    So 870 ms = 870 x 10^-3 s = .87 s

    Or another way to think about this is to multiply the 870ms with the correct ratios to cancel out the ms units so that you are left with seconds :

    870 ms x [tex]\frac{1s}{1000ms}[/tex] = .87s
    Here you are left with seconds; as you can see the milliseconds have canceled out.

    You could continue to convert this into hours:

    .87s x [tex]\frac{1 min}{60s}[/tex] x [tex]\frac{1 hr}{60 min}[/tex] = 2.416...x 10^-4 hr
    Here we are left with hours since the units of seconds and minutes have been eliminated.

    Now for the question:

    [tex]\frac{5300 km}{1 hr}[/tex] x [tex]\frac{1000 m}{1 km}[/tex] x [tex]\frac{1 hr}{60 min}[/tex] x [tex]\frac{1 min}{60 s}[/tex] = [tex]\frac{1472.222 m}{1 s}[/tex]

    [tex]\frac{1472.222 m}{1 s}[/tex] x .87s = 1280.83 m

    1280.83 / 2 = 640.4 m or .64 km
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: The speed of sound
  1. Speed of Sound (Replies: 1)

  2. Speed of sound (Replies: 2)

  3. Speed of sound (Replies: 2)

  4. Speed of Sound (Replies: 5)

  5. Speed of Sound? (Replies: 6)

Loading...