# Question regarding finding velocity give force and mass

Tags:
1. Nov 30, 2015

### jcruise322

Hi,

First time posting here! I have a fairly simple question...but anyway, imagine that a person on planet earth jumps exerting an extra X # of newtons on the surface (uniform force). How would I go about modeling the person's velocity at any time t? Obviously, Vf=Vo+a*t....Instinctively, I would apply the impulse theorem F*Δt=m*Δv to find the velocity immediately after the jump (Vo), but that requires the amount of time that the person's legs are in contact with the ground. Is this possible to do without the time variable? Are there any other ways to do this problem? Maybe make Δt=(Vf-Vo)/a? The net force would just be the extra force generated by the jump (right?), so I could find the acceleration fairly easily that way, and Vo, to the best of my understanding, would be zero.
I have to find Vo, and I don't see any other way.
In any case, thanks for your time, and I would appreciate any input!

JT

2. Nov 30, 2015

### Buzz Bloom

Hi JT:

I have a suggestion, but I am not sure it is helpful.

Instead of of dealing with the time Δt the force is being applied, perhaps you can estimate the distance Δd the center of gravity of the jumper is raised. Then the jumper is gaining kinetic energy f*Δd = (1/2)*m*v2.

Good luck.

Regards,
Buzz

3. Dec 1, 2015

### haruspex

If you wish to assume constant force, Buzz Bloom's method works. But reality might be more like constant power.

4. Dec 1, 2015

### jcruise322

Awesome! Appreciate the responses, guys!!