# Homework Help: Quick Question on mass/spring system

1. Jul 9, 2008

### NBAJam100

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

A 3Kg mass, attached to spring oscillates w/ amplitude of .15m and a period of 2s. At time t= 0.5s the objects position is .019m.

Find the total energy of the system

2. Relevant equations

(.5)mv^2+(.5)kx^2= (.5)kA^2

3. The attempt at a solution

I found the spring constant to be 29.6 N/m... my only question is this... (.5)mv^2+(.5)kx^2
would give me the answer, as would (.5)kA^2 correct? to get the total energy i just did (.5)(29.6)(.15)^2 = .333J

Is that correct???

2. Jul 9, 2008

Yes it is.

3. Jul 9, 2008

### NBAJam100

Thank a bunch rock... i also had one other quick question that i figure ill post here so i dont start another post minutes after this one...

A periodic wave has the equation .15m*sin(10t+(pi)x)

Now i am getting a little bit mixed up about how to determine the direction of the wave... Im going to say this wave is moving in a positive direction because (pi)x is positive... meaning it is going forward... is that correct? So when i rewrite the equation it would be .15m*sin(10t+(pi)(x-vt)) to account for the positive change? Thanks for all of the help guys.