- #1

Mayzu

- 7

- 0

## Homework Statement

(a) An 81 kg student is launched from a bridge by his best friends, some 50 metres above the river surface. Fortunately, he is attached to a 30 m bungee cord with a spring constant of 270 N/m.

i) What is the equilibrium length of the bungee cord, including the force of gravity?

**(I managed to solve this, it's 32.9m)**

ii) What velocity would the student have when he reaches the equilibrium position if he fell in free fall with no air resistance?

**(I can solve this using constant accelaration equations, but can someone tell me how to solve it using energy equations?)**

iii) The student has a velocity of 23 m/s at the equilibrium position. Calculate the maximum extension of the spring from its equilibrium position. Is he safe?

**(Clueless about this one!)**

2. Homework Equations

2. Homework Equations

Usp=1/2kx^2

GPE=mgh

KE=1/2mv^2

## The Attempt at a Solution

I've tried everything!

I have tried taking the equilibrium position of 32.9m as a point of zero GPE (not that I fully understand why you can do this, I just accepted more or less that you can :/)

Then I used that to say

KE(at equilibrium)=1/2*k*(delta)x^2+m*g*(delta)x

This gave me a wrong answer though. The answer is 45.5m. I'm really lost, no one seems to know the answer to this...