Hey guys. I'm trying to figure out the spring constant of a bungee cord. Weight = 80kg Gravity = 9.8m/s/s Length of cord = 10m Length of jump = 50m I've been shown two different methods. And I don't know which one is correct because they give two different answers :/ 1. k = F/x = mg/x Also knows as : k=Fx/x-x0 So i substitute: k= (80kg x 9.8) / (50-10) k= 19.6 N/M 2. PE=mgh KE=0.5mv^2 = 0.5kx^2 F= -kx mgh=0.5kx^2 80 x 9.8 x 50 = 0.5k x 40^2 therefore k= 49 So which method is correct? One gets 19.6, the other gets 49.