# spring mass-undamped

• Oct 8th 2009, 08:30 PM
latavee
spring mass-undamped
A 20-kilogram mass is attached to a spring. If the frequency of simple harmonic motion is 2/pi cycles per second, what is the spring constant k? What is the frequency (in cycles per second) of simple harmonic motion if the original mass is replaced with an 80-kilogram mass?

would omega=sqrt[k/m]
frequency=2/pi so omega=4

what do I do next? or am I totally wrong!?
• Oct 8th 2009, 11:52 PM
CaptainBlack
Quote:

Originally Posted by latavee
A 20-kilogram mass is attached to a spring. If the frequency of simple harmonic motion is 2/pi cycles per second, what is the spring constant k? What is the frequency (in cycles per second) of simple harmonic motion if the original mass is replaced with an 80-kilogram mass?

would omega=sqrt[k/m]
frequency=2/pi so omega=4

what do I do next? or am I totally wrong!?

Write out the equation of the frequency of the spring-mass system in terms of the mass and spring constant:

$\displaystyle f=\frac{1}{2\pi}\sqrt{\frac{k}{m}}$ Hz

You are told that when $\displaystyle m=20$ kg $\displaystyle \ \ f=2/\pi$ Hz so you can solve for the spring constant $\displaystyle k$.

Now you have the spring constant so plug that and a mass of $\displaystyle 80$ kg into the equation for frequency to calculate the new frequency (or just observe that the mass has gone up by a factor of $\displaystyle 4$ so the frequency goes down by a factor of $\displaystyle 2$).

CB
• Oct 9th 2009, 05:22 AM
latavee
Thank you
Thanks, this makes sense now!