Edexcel M3 SHM

Ex3D Q7, Is the book wrong?

Q9 part B, max EPE = max KE, how do I find max EPE?
12/2.4(0.2^2+1.4^2) = 10 is wrong.

Ex3D Q7, Is the book wrong?

Q9 part B, max EPE = max KE, how do I find max EPE?
12/2.4(0.2^2+1.4^2) = 10 is wrong.

@Zacken, wrong forum

I would use $v_{\text{max}} = \omega a \Rightarrow \mathrm{KE_{max}} = \frac{1}{2}mv_{\text{max}}^{2}$ rather than energy considerations.

@iEthan pls.



Please post a picture of the question?

http://www.physicsandmathstutor.com/a-level-maths-papers/m3-solutionbank/
CH3 -> EX3D

Should work both ways right?

Just use $v_{\text{max}} = \omega x_0$ surely?

Yes, using energy considerations worked for me - got an answer of 2.56 J both ways. I'm talking about Q7. I'll take a look at 9 as well. Are you using $\mathrm{KE} = \frac{\lambda a^{2}}{2l}$ and converting everything to m?

EDIT: 9(b) works the same way

Q7A or Q9B?

Both.

..

Q7A or Q9B?

9B-What did you have for max EPE?

Maybe I didn't explain it well.
I have used v=wa and I did get the right answer.
For Q9B, what values did you use for max EPE?

For 9B: $\displaystyle \frac{2 \times 12 \times 0.6^2}{2 \times 1.2} = 3.6$

(12/2.4)(1.4^2-0.2^2) is what I used. No way of finding max EPE by subtracting EPE of the individual springs?

No, you'd need to add E.P.E of each string, it's not a vector quantity so them acting in opposite directions doesn't mean you subtract them. It's like subtracting two E_k's of a particle when you want to find the total E_k, it's not correct, you need to add.