Gracep1
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A vertical steel cable of diameter 24 mm and of length 18m supports a weight of 1500N. Calculate its tensile stress.
Can anyone please explain how to do this?
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Stonebridge
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Have you studied Hooke's Law?
Do you know the definition/formula for stress in terms of force and cross section area?
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Gracep1
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I’ve managed to complete the question I was just stuck as I haven’t been taught it however am now stuck on this one:A steel bar of length 40mm and a cross-sectional area of 4.5 x 10^-4 m^2 is placed in a vice and compressed by 0.2 mm when the vice is tightened. Calculate the compressive force exerted on the bar. How am I meant to work this?
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Stonebridge
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There is missing information here. Why?
Because
It's the same idea except compression rather than stretching.
E = stress/strain =  \frac{ (F/A)}{(x/L)}
You are given, x, L and A but need E, the Young's Modulus, for the wire to be able to solve this for F.
Is it provided somewhere else on a data sheet or another part of the question?
Last edited by Stonebridge; 6 days ago
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Gracep1
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(Original post by Stonebridge)
There is missing information here. Why?
Because
It's the same idea except compression rather than stretching.
E = stress/strain =  \frac{ (F/A)}{(x/L)}
You are given, x, L and A but need E, the Young's Modulus, for the wire to be able to solve this for F.
Is it provided somewhere else on a data sheet or another part of the question?
Yes i am given the youngs modulus. It says the is it a steel wire so i gave E as 2.1 x 10^11
i worked the question out by using extension/length = strain
then using young modules x strain = stress which got me 4.7 x 10^6 N
did i do this correctly?
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Stonebridge
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Yes that's right but one more step. The 'stress' from using (Young Mod) x (strain) is force/ area
so it does not directly calculate the force. You get that from stress = force / area
with the cross-sectional area being given in the question.
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Gracep1
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(Original post by Stonebridge)
Yes that's right but one more step. The 'stress' from using (Young Mod) x (strain) is force/ area
so it does not directly calculate the force. You get that from stress = force / area
with the cross-sectional area being given in the question.
Okay I think I get it now, thank you for your help
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