# Energy of motion

1. Feb 23, 2009

### nlkush

1. The problem statement, all variables and given/known data
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?
in J.

2. Relevant equations

3. The attempt at a solution

2. Feb 23, 2009

### harvellt

people are gonna ask you to give it a shot be for they help. Lets start with what equations should you use>

3. Feb 23, 2009

### 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!

4. Feb 23, 2009

### 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

5. Feb 23, 2009

### 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.

6. Feb 23, 2009

### nlkush

i see, i still cannot get the right answer i dont no waht im doing wrong

7. Feb 23, 2009

### nlkush

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