# Can I calculate modulus of elasticity without knowing cross-sectional area?

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#1
'An elastic spring of natural length 1.5 m has one end attached to a fixed point.
A horizontal force of magnitude 4 N is applied to the other end and compresses the spring to a length of 1 m.
Find the modulus of elasticity of the spring.'
How do I calculate the modulus of elasticity without the cross-sectional area of the spring? I'm aware λ = stress/strain, but to find stress I believe i need cross-sectional area.
Any ideas how I can solve the problem?
0
1 month ago
#2
Hooke's law I think?
T = kx where k=modulus of elasticity/natural length, T=force and x=extension
Last edited by jamiet0185; 1 month ago
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1 month ago
#3
Think it must mean spring constant... Or else theres a diagram or another section of the question that you dont know about
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1 month ago
#4
(Original post by Joinedup)
Think it must mean spring constant... Or else theres a diagram or another section of the question that you dont know about
Can you not calculate K using Hooke's law then find the modulus of elasticity since K=modulus of elasticity/natural length?
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1 month ago
#5
The question is badly written. Modulus of elasticity or Young's modulus is a property of the material, and the question doesn't sufficient information to calculate it. It looks like they meant to say spring constant as previous posters have suggested.
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1 month ago
#6
(Original post by Hallouminatus)
The question is badly written. Modulus of elasticity or Young's modulus is a property of the material, and the question doesn't sufficient information to calculate it. It looks like they meant to say spring constant as previous posters have suggested.
This

Modulus of elasticity is a property of a material
Spring constant is a property of a spring (made of that material)

an analogy if you've done resistivity

resistance is a property of a resistor
resistivity is a property of a material

you can calculate the resistance of a piece of wire from PD and current... but you can't say anything about the resistivity until you know something about the length and cross sectional area of the wire the resistor is made of.
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1 month ago
#7
(Original post by jamiet0185)
Can you not calculate K using Hooke's law then find the modulus of elasticity since K=modulus of elasticity/natural length?
I would have thought the same. You have a thrust, natural length and compression so T = (modulus of elasticity/natural length) * compression. Just rearrange to find modulus of elasticity
Last edited by Toast210; 1 month ago
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