# Homework Help: Simple Harmonic Motion - Another quick question, sorry

1. Mar 15, 2008

### meganw

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

A fisherman's scale stretches 3.4 cm when a 3.3 kg fish hangs from it.

(a) What is the spring constant?

(b) What will be the amplitude and frequency of vibration if the fish is pulled down 2.5 cm more and released so that it vibrates up and down?

2. Relevant equations

I know that the PE of a spring is .5kA
I also know that x=Asinwt

But I don't know t, so I can't see how I'd use that equation either.

3. The attempt at a solution

I know that equation, but how can I set it equal to the KE of the spring when I don't know the velocity of the spring at all?? I thought this might be a conservation of energy problem but I don't see how that would work out.

Last edited: Mar 15, 2008
2. Mar 15, 2008

### Hootenanny

Staff Emeritus
Have you met Hooke's law yet?

3. Mar 15, 2008

### meganw

I got it right now, (thank you!! =) But how do you find the amplitude on part b?? I don't know the PE, or time....

I'm sorry we just learned this and I'm really confused still.

Last edited: Mar 15, 2008
4. Mar 15, 2008

### Hootenanny

Staff Emeritus
But surely you can just see the amplitude, it's given to you in the question..
Not a problem, and you don't have to apologise for asking questions, you should always ask questions

5. Mar 15, 2008

### Snazzy

The amplitude of a SHM system is how far the object has been stretched from it's initial position.