1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Simple Harmonic Motion (SHM) question check

  1. Aug 24, 2012 #1
    1. The problem statement, all variables and given/known data
    A metal sphere of mass 0.20kg is hung from a helical spring whose top end is clamped. the sphere is displaced by 0.030m below its equilibrium position, and then released. 20 cycles of oscillation, of amplitude 0.030m, occur in a time of 12.0s.
    (I) the spring stiffness, k. (force per unit extension)
    (II) the maximum velocity of the sphere as it oscillates.
    (III) the maximum acceleration of the sphere as it oscillates.

    2. Relevant equations

    3. The attempt at a solution
    my workings;
    (I) W=2*∏/T
    W= 3.76rads-1

    = 0.20/14.14
    k=1.41*10^-2 Nm-1

    (II) Vmax= +- W √A^2 - x^2
    but x=0 so
    Vmax= +- WA
    = +- 3.79 * 0.030
    Vmax= +- 1.13*10^-1 ms-1

    (III) amax= +- W^2 * x
    but x=A so
    amax= +- W^2 * A
    = +- 3.76^2 8 0.030
    amax= +- 4.24*10^-1 ms-2

    could you please check my answers for me, because, i don't know why, i just feel like I've gone wrong somewhere.
    thanks sarah x
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Aug 24, 2012 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Welcome to PF;

    (I) Reasoning looks OK.
    How did you calculate T=1.67(s?)
    In 12 seconds you get 20 cycles - how much time for one cycle?

    Usually better to combine equations before putting the numbers in - to avoid rounding errors.

    (II) and (III) OK reasoning ... you should keep the direction (+/-) since they ask for "velocity" rather than speed.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook