# Homework Help: Breaking Point for a Copper Wire

1. Nov 3, 2005

### Ike

What is the maximum load that could be suspended from a copper wire of length 1.9 m and radius 1.2 mm without breaking the wire? Copper has an elastic limit of 2.9 x 10^8 Pa and a tensile strength of 4.3 x 10^8 Pa. Give your answer in Newtons (N).

Any thoughts? I'm completely lost.

2. Nov 3, 2005

### Pengwuino

Well you may want to start by converting the Pascals to its other SI units (part of it is in Newtons....). That should make it a bit more apparent.

3. Nov 3, 2005

### Ike

My main problem here is this...
When a wire is stretched, it will return to it's original length if the weight is removed. This is true, unless the elastic limit has been reached, in which case the wire will be permanently stretched. Before this point, the proportional limit is met, in which the tensile strain and the tensile stress are no longer proportional. Further beyond the elastic limit is the point of ultimate strength. I assume this is the same as tensile strength. Further beyond this point is the breaking point.

I have no idea how to derive the breaking point at all, nor how to find the maximum weight before that point for that matter.

4. Nov 3, 2005

### Ike

Oh yes, and one Pascal is the same as one Newton per square meter.

1 Pa = 1 N/m^2

5. Nov 4, 2005

### FredGarvin

Since you are only given the elastic limit (yield point) the problem assumes that the onset of yielding will be the breaking point.

You should start looking at what the definition of stress is. If you set the stress in the wire equal to the elastic limit...

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