Confusing (but surely simple) gravity problem

[vysis]

Homework Statement

An exceptional vertical jump from rest would raise a person 0.80m off the ground. To do this, what constant force would a 70kg person have to exert against the ground? Assume the person lowers himself 0.20m prior to jumping and remains in a standing position while in the air.

Homework Equations

F(net)=ma?

The Attempt at a Solution

Not a clue...

 

[Dr. Jekyll]

It's easy to say: "Not a clue..."

Maybe https://www.physicsforums.com/showthread.php?t=225490" will help (as it already did). It's almost the same.

You need the velocity at which man must leave the ground to reach the height of 0.8 m (you know the g). Therefore you can calculate the acceleration and the force.

 

[vysis]

Lol, thank you soooo much (again!)