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# Direct Proportion Tweet

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1. Direct Proportion
The extension E of an elastic string (in mm) is directly proportional to the mass m on the string (in grams)

a) Find a formula for E in terms of m

The numbers that I have been provided are

750g and 35mm

So from what I know

e=km where K is the constant

so 35/750

Which is totally wrong when looking at the answers.

I don't know what I am doing wrong though.

Any Ideas?
2. Re: Direct Proportion
(Original post by zed963)
The extension E of an elastic string (in mm) is directly proportional to the mass m on the string (in grams)

a) Find a formula for E in terms of m

The numbers that I have been provided are

750g and 35mm

So from what I know

e=km where K is the constant

so 35/750

Which is totally wrong when looking at the answers.

I don't know what I am doing wrong though.

Any Ideas?
But what do the numbers you have been given actually represent?
3. Re: Direct Proportion
Actually let me think
4. Re: Direct Proportion
(Original post by Cephalus)
But what do the numbers you have been given actually represent?
the extension of the string is 35mm and the mass on the string is 750g
5. Re: Direct Proportion
Are you sure your formula is correct?
6. Re: Direct Proportion
(Original post by Cephalus)
Actually let me think
what would the force be?
7. Re: Direct Proportion
Well I was thinking of Hookes law where the force is equal to the weight if it was hanging vertically

hookes law states force = k multiplied by extension
Last edited by Cephalus; 03-08-2012 at 16:56.
8. Re: Direct Proportion
What does the answer say?
9. Re: Direct Proportion
Can you give the full question

In particular I want to know if 35 is the length or the extension

sorry missed post 4

Full Q may still be handy though
Last edited by TenOfThem; 03-08-2012 at 17:01.
10. Re: Direct Proportion
(Original post by TenOfThem)
Can you give the full question

In particular I want to know if 35 is the length or the extension
Not unless he thinks he's wrong because he hasn't cancelled his fraction? But yeah mixing up length and ext is the most common mistake I suppose.
11. Re: Direct Proportion
Is it simply because you haven't simplified your fraction?
In that case, the final answer would be 7/150.

Either that, or we are missing the full question.
12. Re: Direct Proportion
(Original post by Codecharacter)
Is it simply because you haven't simplified your fraction?
In that case, the final answer would be 7/150.

Either that, or we are missing the full question.
Yes that is the correct answer but where have you got that from,

Please can you show me your full working out.
13. Re: Direct Proportion
Oh you just simplified it ignore post 12 codecharacter.
14. Re: Direct Proportion
(Original post by zed963)
Oh you just simplified it ignore post 12 codecharacter.
Remember to simplify next time lol
15. Re: Direct Proportion
(Original post by Codecharacter)
Remember to simplify next time lol
I just entered the thing in the calculator and it turned into a decimal, I should have converted it into a fraction instead, my bad.

Thanks,