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# Engineering maths help watch

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1. Hey, i am studying for my engineering materials exam, first year undergrad.

What is the minimal diameter of a copper wire that can support the mass of 100 kg without breaking?
The Young’ modulus of copper is 120 GPa, yield strength 190 MPa
and tensile strength 250 MPa.

I know to find the maximum diameter i have to use the tensile strength although using stress=force/area and i need to find diameter i'm not actually given force and need to find area which cant be found from the yield stress because i imagine the diameter for yield stress will be different than for tensile stress. Any help would be great, thanks !!
2. (Original post by Engclasshelp)
Hey, i am studying for my engineering materials exam, first year undergrad.

What is the minimal diameter of a copper wire that can support the mass of 100 kg without breaking?
The Young’ modulus of copper is 120 GPa, yield strength 190 MPa
and tensile strength 250 MPa.

I know to find the maximum diameter i have to use the tensile strength although using stress=force/area and i need to find diameter i'm not actually given force and need to find area which cant be found from the yield stress because i imagine the diameter for yield stress will be different than for tensile stress. Any help would be great, thanks !!
engineering forum if there is such place must be better
3. first find the weight on the copper wire using f=ma.

you know that stress = force / area, i.e.

rearrange to find the area:

substitute in what you know:

area of a circle is:

rearrange to find the diameter:

and so

i'm just guessing so i might be wrong.
4. (Original post by samsama)
first find the weight on the copper wire using f=ma.

you know that stress = force / area, i.e.

rearrange to find the area:

substitute in what you know:

area of a circle is:

rearrange to find the diameter:

and so

i'm just guessing so i might be wrong.
Thanks so much!!
5. (Original post by Engclasshelp)
Hey, i am studying for my engineering materials exam, first year undergrad.

What is the minimal diameter of a copper wire that can support the mass of 100 kg without breaking?
The Young’ modulus of copper is 120 GPa, yield strength 190 MPa
and tensile strength 250 MPa.

I know to find the maximum diameter i have to use the tensile strength although using stress=force/area and i need to find diameter i'm not actually given force and need to find area which cant be found from the yield stress because i imagine the diameter for yield stress will be different than for tensile stress. Any help would be great, thanks !!
Moved to Engineering forum
6. thx but your second to the last step, your rearranging is wrong

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