Hey! Thanks for attempting it. A quicker way I've found to use this is using energy conservation, where the energy at the starting position is equal to the energy at the bottom of the bungee cord. In VCE Physics, unless stated otherwise, we assume that all energy is converted to elastic potential energy at the bottom of her jump. So from this energy at top = energy at bottom. Given she's standing from a height, we can use her gravitational potential to calculate her energy at the top. As such, mgh = ½k(x

^{2})

Remember that given the bungee cord is will stop after a distance of 60m, so we use that as her height. So first step is to calculate gravitational potential energy

Gravitational potential energy = mgh

mgh = 50kg * 9.8ms

^{-2} * 60m = 29,400 J

Note that the cord only stretches for 20m, as stated in the question, so for the elastic potential energy, x = 20m

mgh = ½k(x

^{2})

∴ 29,400 J = ½k(20m

^{2})

∴ k = 147 N/m

For these sorts of questions, it might be quicker to use conservation of energy. This is the method VCAA prefer use to use, as shown in past exam solutions (example: 2006 Physics Exam 1, Question 14)