A bungee cord is 45.0m long when un-streched. A 1.70m tall jumper (mass 70kg), with both feet tied to the cord, falls from a bridge 85m above the river. If the jumpers head just touch the water at the lowest point.
1) What is the force k of the bungee cord
2) what is the speed of the jumper when he/she is 55.0m below the bridge?