Energy of Motion: 2.4kg-mass w/ 7.0cm amp & 5.0Hz freq

[nlkush]

Homework Statement

A 2.4kg- mass attached to a spring oscillates with an amplitude of 7.0cm and a frequency of 5.0Hz .
What is its energy of motion?
Express your answer using two significant figures.
in J.

Homework Equations

The Attempt at a Solution

 

[harvellt]

people are going to ask you to give it a shot be for they help. Let's start with what equations should you use>

 

[Delphi51]

You have two energy formulas that apply:
E = 1/2*k*x^2 for when the spring is stretched but the bob is not moving.
E = 1/2*m*v^2 when the object is moving but the spring is not stretched.
Looks like the first one will be easier to work out!

 

[nlkush]

ok i have my T which is 0.2s
omega is 31.4
k is 2366.3
and amplitude is 7
eqn to be used is E=1\2kA(squared) i believe but i cannot get the correct answer doing so

 

[Delphi51]

I haven't seen E = 1/2*k*x^2 written with an A instead of an x.
The x means "extension" or how much the spring is stretched.
Or compressed.
That just means the 7 cm, I think.

As the spring oscillates, this energy is repeatedly converted back and forth between spring energy and kinetic energy. If you knew the maximum speed of the bob, you could use E = 1/2mv^2 and get the same answer. Or you could set 1/2*k*x^2 at maximum extension equal to 1/2mv^2 at maximum speed and solve for the speed.

 

[nlkush]

i see, i still cannot get the right answer i don't no what I am doing wrong

 

[nlkush]

my answers come to 580 or 5.8*10^5
and it comes up wrong