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: Physics 20 Waves and Motion Questions?

  1. Oct 17, 2011 #1
    1. The problem statement, all variables and given/known data
    A tourist shouts across a canyon. The sound wave she creates travels at 350 m/s across the canyon and reflects off the opposite rock wall. She hears the echo 0.981 s after she shouts. Calculate the width of the canyon.

    2. Relevant equations

    Im not sure what the formula is really called, but you guys know what cross multiply and divide is, right? X1/X2 = Y1/Y2

    3. The attempt at a solution

    350/1=x/0.981 (where we solve for "x" where 350 is in meters and 1 , and 0.981 is in seconds )
    I got 343.35m as the answer, which means that the distance from the person, to the wall, and back is the distance i wrote, so if i divide it by 2, will that be the width of the canyon?
    343.35/2=171.675m the width of the canyon.

    The next one is
    1. The problem statement, all variables and given/known data
    The formula for the period of a pendulum with small angles is
    T=2 π√m/k
    Derive the formula for "m"

    2. Relevant equations
    T=2 π√m/k
    3. The attempt at a solution
    I know i had to do some basic algebra, so
    T = 2 π√m/k
    T/2π = √m/k
    (T/2π)^2 = m/k
    (T/2π)^2 k = m
    m = (T/2π)^2 k
    Is this the right formula for "m" i am really bad at algebra!
    Thank You for any help! This is my first post, i just inherited this account from my sister who doesn't use it anymore!
  2. jcsd
  3. Oct 18, 2011 #2
    it takes 0.981s for the sound to travel 2W and the sound is traveling at 350m/s

    Not sure exactly what your second question wants. If it is just in terms of m instead of the period then you're right
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook