# Tension Question?

1. Sep 6, 2008

### cremedelacreme

Two steel wires P and Q have lengths l and 2l respectively and cross sectional areas A and A/2 respectively. Both wires obey Hooke's Law.

What is the ratio (tension in P/tension in Q) when both wires are stretched to the same extension?

2. Sep 7, 2008

### Redbelly98

Staff Emeritus
You must show an attempt at solving this before we can help you (forum rules).

3. Sep 7, 2008

### cremedelacreme

Yeah, I got it but it's not the right answer...

4. Sep 7, 2008

### Hootenanny

Staff Emeritus

5. Sep 7, 2008

### cremedelacreme

F/A divided by Difference in L/L

Since
Stress/Strain

Thus Fl/A(Difference in L)

L is doubled

Area is halved
hence in Q it should be 4
while in P it is 1

But the answer says that it is 4:1

6. Sep 7, 2008

### Redbelly98

Staff Emeritus
That's a good attempt, you're very close.

Stress/Strain must be the same for both wires, since that is Young's Modulus for the material.

As you said, (L/A) is a factor of 4 larger for Q.

What must F be for wire Q, in order that the ratio
F L/(A ΔL)
be the same for both wires?