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: Checking over SHM

  1. Jan 6, 2005 #1
    The intensity of a spherical wave is 21 W/m^2 at a distance 16 m away from a constantly emitting source. What will it be 3 m away?

    Using the formula

    I_2/I_1 = (r_1)^2/(r_2)^2

    I got 588 W/m^2 0r 600. Correct?

    If the length of pendulum with T = 10 s were halved, what would be its new T?

    My answer was 7.1. Correct?

    Halved scenario:

    T = 2pi*sqrt(L/2g)

    but first find original L with

    10 s = 2pi*sqrt(L/9.8) to plug in.

  2. jcsd
  3. Jan 6, 2005 #2
    first answer is correct: I is proportional to the inverse square since the source emits energy in spherical wave fronts and the surface area of a sphere is 4*pi*r^2.

    the second anser sounds good but i havent a calculator near me. The period of a pendulum is proportional to the square root of the length so T1/T2=(L1/L2)^.5 so the answer reduces to 10/2^.5 or 10/1.4
  4. Jan 7, 2005 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The second is right too.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook