Different young modulus of rod - Need a proper explanation?

AI Thread Summary
The discussion revolves around calculating the maximum tensile stress that can be applied to a composite rod made of two materials with different Young's moduli before it breaks. The rod has a total extension limit of 3.0 mm, and the Young's modulus equation (stress = strain × modulus) is central to solving the problem. Participants emphasize that the combined extension of both materials must not exceed this limit, regardless of which material fails first. Understanding how each material stretches under the same stress is crucial for determining the maximum allowable stress. The key takeaway is that the focus should be on the total extension rather than the individual material failure.
PhysicStud01
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Homework Statement


A rod is made up as shown [pic attached]
pic.png

Both have same cross-sectional area. Ep and En are Young modulus.
The rod breaks when total extension = 3.0mm
Greatest tensile stress that can be applied before rod breaks?

Homework Equations


Young modulus = stress / strain

The Attempt at a Solution


Ans: 5.7 x 10^6 Pa.
Won't it break when the one of the 2 materials breaks? Can you please tell me the concepts to be used. How to solve?
Thanks
 
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PhysicStud01 said:

Homework Statement


A rod is made up as shown [pic attached]
View attachment 75901
Both have same cross-sectional area. Ep and En are Young modulus.
The rod breaks when total extension = 3.0mm
Greatest tensile stress that can be applied before rod breaks?

Homework Equations


Young modulus = stress / strain

The Attempt at a Solution


Ans: 5.7 x 10^6 Pa.
Won't it break when the one of the 2 materials breaks? Can you please tell me the concepts to be used. How to solve?
Thanks

The Young's modulus tells you how much the material stretches for a given applied tensile stress.

If you apply the same stress to the rod shown in the OP, which material is going to stretch more?

The problem is asking you to find how much stress can be applied to the rod so that the combined stretch of the nylon and the glass-reinforced plastic equals 3 mm. Remember, the strain is equal to the change in length of the material divided by the original length (unstretched).
 
PhysicStud01 said:
Won't it break when the one of the 2 materials breaks?
Sure, but you don't care which breaks, or even the fact that it breaks. What matters is that the max allowed extension of the rod as a whole is 3mm.
 
Thread 'Collision of a bullet on a rod-string system: query'

Thread 'Collision of a bullet on a rod-string system: query'

In this question, I have a question. I am NOT trying to solve it, but it is just a conceptual question. Consider the point on the rod, which connects the string and the rod. My question: just before and after the collision, is ANGULAR momentum CONSERVED about this point? Lets call the point which connects the string and rod as P. Why am I asking this? : it is clear from the scenario that the point of concern, which connects the string and the rod, moves in a circular path due to the string...
View full post »

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