Question reads: An exceptional vertical jump from rest would raise a person 0.80m off the ground. to do this what constant force would a 70.0 kg person have to exert againts the ground. Assume the person lowers himself by 0.20m prior to jumping and remains in a standing position while in the air. My progress: well firstly i drew a free body diagram of him on the floor. (Fn[up] and Fg[Down]) and when he is in the air (Fg[Down]) then i tried finding out the velocity and hopefully i can find acceleration afterwards. i used vf^2 = vi^2 + 2ad i set accelration as (-9.8m/s^2) because once he is in the air gravitational force pulls him down. am i going in the wrong direction ? where should i begin this problem. im also confused why crouching 0.20m prior to jumping would change anything. please further guide me with this problem. thanks.