Force Exerted From the Ground During a Jump.

[JSpadafore]

Hello! This problem has been driving me crazy all week long, and now I am down to the last few hours before the assignment is due. Any help would be greatly appreciated!

Homework Statement

An average person can reach a maximum height of about 60cm when jumping straight up from a crouched position. During the jump itself, the person's body from the knees up typically rises a distance of around 50cm. To keep the calculations simple and yet get a reasonable result, assume that the entire body rises this much during the jump.

Part A required me to find the initial speed a person would need to reach a maximum height of 60cm, for which I correctly answered 3.4m/s.

Part B is where I find myself stuck. It asks, "In terms of this jumper's weight (w), what force does the ground exert on him or her during the jump?"The answer will read:
F= ___ w.

Homework Equations

ƩF_y=ma_y
w=mg
...

The Attempt at a Solution

Honestly, I've just been trying to figure out how I am supposed to get anywhere without first knowing the mass of the person jumping. I suspect it has something to do with the initial speed I had calculated for Part A being related to an opposite force, coming from the ground going to the person jumping.

 

[ehild]

The body accelerates from zero to 3.4 m/s speed during the first stage of the jump, while rising 0.5 m. Determine the acceleration. From the acceleration, you can find the force.

ehild

 

[Doc Al]

Honestly, I've just been trying to figure out how I am supposed to get anywhere without first knowing the mass of the person jumping.

You are asked to express the answer in terms of the jumper's weight. So given the weight as W, what's his mass?