Please I really need help on this problem Essentially on que

Please, I really need help on this problem. Essentially on question # 20.

I need a explanation, not only the answer.

At what height above the ground should the skydiver open his parachute if his speed jus before landing is to be 5.00 m/s ?

Thank you.

Solution

By the conservation of the energy absorbed by the parachut when open and when closed and the kinetic eenrgy he pocessess just before he fall to ground must be equal to the total potential energy he gained by climging the height h

               Potential energy mgh = F * h1 + Fp * h2 +mv^2 / 2      , h1 + h2 = 1200 m

                          F *h1 = energy lost with out parachut , Fp * h2 = energy lost with parachut , and h2 is height at which parachut released ,          mv ^2 / 2 = kinetic energy he should pocessess

823200 = 40 (1200-x) + 3600N * x +    70 * 5 ^2 / 2         

                             823200 = 48000 - 40 x + 3600 x + 875

                                             x = 218.911