- #1

ehralley

- 1

- 0

## Homework Statement

An angler hangs a 5.50 kg fish from a vertical steel wire 1.30 m long and 4.32×10^-3 cm in cross-sectional area. The upper end of the wire is securely fastened to a support.

Calculate the amount the wire is stretched by the hanging fish. (I found this to be 8.11x10-4 m)

The angler now applies a force F to the fish, pulling it very slowly downward by 0.569mm from its equilibrium position. For this downward motion, calculate the work done by gravity. (I found this to be 3.07x10^-2 J)

For this downward motion, calculate the work done by the force F.

## Homework Equations

E=FL_0/A_0ΔL

W=Fd

My prof reccomended using: k=EA_0/L_0 and W=0.5kx^2

## The Attempt at a Solution

Using Young's Modulus, F=EA_0ΔL/L_0

F=(2x10^11 N/m)(4.32x10^-7 m ^2)/(1.300811 m)

Solving for F=37.8 N

W=Fd

W=(37.8 N)(0.000569 m)

W=2.2x10^-2 J

Then I emailed my prof and he said to do it like this:

k=EA_0/L_0

k=(2x10^11 N/m)(4.32x10^-7 m^2)/(1.300811 m)

k=66420 N/m

W=0.5kx^2

W=(0.5)(66420 N/m)(0.000569 m)^2

W=1.08x10^-2 J

According to Mastering Physics, both of these answers are wrong. Please Help!