# Homework Help: This'll be quick-For an oscillating object as shown,it's graph of Ep/J against t/s ?

1. Jun 9, 2007

### inv

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

Hi,the question is draw a graph of $$E_{p}$$ against t/s of the oscillating motion above,I've done it and have no exact answer in my hand,hoping some ppl to double check my answer that's all.My answer is here below

2. Relevant equations
$$E_{p}$$=mgh , where $$E_{p}$$ is potential energy,m=mass,g=gravitational pull,h=height

3. The attempt at a solution

Correct?!

Last edited: Jun 9, 2007
2. Jun 9, 2007

### chaoseverlasting

You see, Ep=mgx, where x is the height of the end of the strip. Now, since the motion is simple harmonic (from the graph), x=A sin(wt) (equation of shm), therefore, Ep=mgA sin(wt), which can be rewritten as Ep=B sin(wt), where B is a constant (mgA). From this it seems that your solution is incorrect... The graph will look like fig 4.3, but the amplitude will be different...

3. Jun 9, 2007

### inv

Well I've drawn my amplitude all above x-axis as the $$E_{p}$$ starts from 0-origin,then increases to max then back to zero again,forming a sinusoidal wave type pattern.The graph requested didn't put a requirement to be exact in amplitude.How different u mean?

4. Jun 9, 2007

### chaoseverlasting

Different as in, taking the potential when the rod is at the mean position to be zero, the graph should be above and below the curve.

5. Jun 9, 2007

### esalihm

your answer is correct but what people are saying that u are missing the values on the y axis, they are not the same values as on the first graph,
but the shape of the curve is correct,

because the starting point is 0, no it does not go above and below the x axis

6. Jun 10, 2007

### inv

Hey thx a bunch!Solved!**