- #1

Abid Rizvi

- 20

- 0

## Homework Statement

A daredevil plans to bungee jump from a balloon 59.0 m above the ground. He will use a uniform elastic cord, tied to a harness around his body, to stop his fall at a point 13.0 m above the ground. Model his body as a particle and the cord as having negligible mass and obeying Hooke's law. In a preliminary test he finds that when hanging at rest from a 5.00-m length of the cord, his body weight stretches it by 1.65 m. He will drop from rest at the point where the top end of a longer section of the cord is attached to the stationary balloon.

## Homework Equations

Hookes Law = 1/2 kx^2

Potential Energy = mgx

## The Attempt at a Solution

Okay so for starters I said when he falls out of the balloon he falls a distance x at which he is now not falling.

x = 59-13 = 46

Then I set out to find k for Hookes law. I said mg = ky where y is the 1.65 m. So

k = (mg)/y

I then said r is the actual length of the chord, and L is the length that the chord stretches. So

r + L = x

I then said the total potential energy of the devil is mgx, and the amount of work in opposition to him by the chord is 1/2KL^2 = 1/2 * (mgL^2)/y

I set this equal to mgx: 1/2 * (mgL^2)/y = mgx

= (L^2)/(2y) = x

= L = sqrt(2yx)

solving for L and subtracting it from x to get r (the actual length of the chord) I get 37.3 m. Which apparently is wrong. What am I missing? Thanks in advance