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!

Simple harmonic motion and frequency; answer disagrees from answer key

  1. Nov 24, 2008 #1
    1. The problem statement, all variables and given/known data

    A block attached to a spring oscillates in simple harmonic motion along the x axis. The limits of its motion are x = 10 cm and x = 50 cm and it goes from one of these extremes to the other in 0.25 s. Its amplitude and frequency are:

    A) 40 cm, 2 Hz
    B) 20 cm, 4 Hz
    C) 40 cm, 2 Hz
    D) 25 cm, 4 Hz
    E) 20 cm, 2 Hz

    2. Relevant equations

    [tex]T = 1/f[/tex]

    3. The attempt at a solution

    I got the amplitude correct by adding the limits and dividing by two to find the midpoint of the motion, which was 30 cm, which I took to be equilibrium. Then I subtracted 10 cm, one limit of motion, from 30 cm, equilibrium to get the amplitude of 20 cm.

    The frequency is where I mess up. I multiplied .25s by 2, since I thought it takes .25 seconds to complete half the cycle; I thought it must go back to the same extreme to complete a cycle, and thus would take another .25s. I got .5s for the period and then took the reciprocal of .5 for a frequency of 2 Hz.

    The answer key however says the answer is B, a frequency of 4 Hz. Is this a mistake of the answer key or on my part? I do not see why the frequency would be 4.
  2. jcsd
  3. Nov 24, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    I'd say that you are correct and the answer key is wrong.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?