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?