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M2 - Elasticity

I'm on question 14 below. The answer for AM is 2.99m but I'm getting 2.96m.

What am I not doing properly, please?
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BabyMaths
Original post by maggiehodgson
I'm on question 14 below. The answer for AM is 2.99m but I'm getting 2.96m.

What am I not doing properly, please?


I'm not sure where you have gone wrong but I would have considered e1+e2=1e_1+e_2=1.

My equation for this problem is 100(x−2)2−20(4−x−1)=5g\dfrac{100(x-2)}{2}-20(4-x-1)=5g. This leads to the solution you gave. Can you see how I obtained this?

Hope this helps but if not hang on for ghostwalker's always superior explanation. :smile:
Original post by BabyMaths

Hope this helps but if not hang on for ghostwalker's always superior explanation. :smile:


:blush:

Original post by maggiehodgson

What am I not doing properly, please?


You assumed that the top spring would be stretched and the bottom one compressed, which in itself is not a problem - though you have to be more careful thereafter.

When working out T2T_2 the extension is "−e2-e_2". If you go with that it will work out correctly.

It is far easier, as BabyMaths did and I would do, to assume both springs are stretched.
(edited 9 years ago)
Original post by BabyMaths
I'm not sure where you have gone wrong but I would have considered e1+e2=1e_1+e_2=1.

My equation for this problem is 100(x−2)2−20(4−x−1)=5g\dfrac{100(x-2)}{2}-20(4-x-1)=5g. This leads to the solution you gave. Can you see how I obtained this?

Hope this helps but if not hang on for ghostwalker's always superior explanation. :smile:



That is so obvious now that you've told me.

Thank you.
Original post by ghostwalker
:blush:



You assumed that the top spring would be stretched and the bottom one compressed, which in itself is not a problem - though you have to be more careful thereafter.

When working out T2T_2 the extension is "−e2-e_2". If you go with that it will work out correctly.

It is far easier, as BabyMaths did and I would do, to assume both springs are stretched.


It all makes sense. I will remember that for future.

If I did it my way, MB compressed, I'm thinking then T2 would be Thrust not Tension so T1+T2 = 5g? I'll give that a go and see if it's true.

However, I'll redo my drawing and do it the obvious way for my notes.

Thanks.
Original post by maggiehodgson

If I did it my way, MB compressed, I'm thinking then T2 would be Thrust not Tension so T1+T2 = 5g? I'll give that a go and see if it's true.


Yep, that's another way to deal with it.

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