Question

A person wants to participate in a bunjee jump. One end of an elastic band 10m long with a spring constant of 50N/m will be attatched to a basket on a crane and the other end to the waist of the person with a mass of 86kg. The person will step off the edge of the basket to be slowed and brought back by the elastic band before hitting the ground (hopefully 2m above) How high should the crane be? (hint: conservation of energy).

I know I use this equation but I am confused on how to solve for h when there is h on both side of the equation?
MgH = (1/2)*k*(H-2-10)^2 + Mg*2

Answer 1

expand the square on the right, gather terms, put it in the standard quadratic form, and use the quadratic formula.

Answer 2

I get 54.5 when I caculate the answer