Proving 5G in G-Max Reverse Bungee in NZ & SG

[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?

 

[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?

 

[wintergirl]

thanks for your reply. ;D
i understand what you are trying to say.
and er no, actually we arent given anything. this is sort of a project, where we are supposed to find out about the topic then write an article on it. we haven't even been taught about G, only about acceleration. =(
is it possible to not include spring constant?

PS: sorry everyone, i know i haven't shown much trying in my work, but the thing is i have no idea where to start with since it wasnt taught...pls bear with me. thanks a load!