# Homework Help: About reverse bungee

1. Sep 15, 2007

### wintergirl

1. there is such a reverse bungee machine called the G-max Reverse Bungee in New Zealand and Singapore. Basically it works by attaching a car to two stretched giant rubber bands, then releasing them from the ground, so that it rockets up (to 60m), quite like reversed bungee jumping. it claims to be able to achieve 5 G, and we are supposed to prove it.

2. we are allowed to assume the mass of the car and the people sitting in it. there was no given equation but i found this on wikipedia.
g=-[(MG)/r^2]R
where:
r is the vector from center of the object to the location we are considering, and
G is the gravitational constant of the universe.

3. so assuming the weight of the car + 3 people is 800kg, we can substitute to solve. but what does r mean? or alternatively, does anyone have a better solution to prove that it reaches 5G?

Last edited: Sep 15, 2007
2. Sep 15, 2007

### Mindscrape

You won't have to use the gravity formula, and can just assume it is 9.8m/s^2. 5Gs means 5 times the acceleration of gravity, so you are looking to see if the bungee cords can accelerate the car to 5*9.8m/s^2. You will want to use Newton's second law for the forces from gravity and the spring. Are you given a spring constant, or is that what you are supposed to be solving for to see if it is reasonable?

3. Sep 15, 2007