Biomechanics question vertical velocity

[Rachel79]

Homework Statement

Jenna is standing still when her dancing partner, Tyrel, begins to lift her up and throw her into the air. Jenna's mass is 40 kg. Tyrel exerts an average vertical force of 500 N for 0.8 s on Jenna during the lift and throwing motion. What is Jenna's vertical velocity when Tyrel releases her? Use g = -9.8 m/s2.

Homework Equations

The problem is that I am not sure which equation to use. I thought about using the Maximum Height equation, but I can't get an answer that works with that.

The Attempt at a Solution

.8(500)=40 (change in Velocity)
-10^2/2(-9.8) +.8
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[MarkFL]

Okay, let's consider the kinematic equation:

$v(t)=at+v_0$

In order to determine the acceleration $a$, we need to examine the net force on Jenna...if we orient our coordinate axis such that Jenna begins at the origin, and the positive direction is up, we know the fore exerted by Tyrel is positive, and Jenna's weight is negative (points down)...can you state the net force on Jenna?

 

[haruspex]

.8(500)=40 (change in Velocity)

Force x time does not give a velocity. What does it give?
And even if Tyrel just held her slightly off the ground he would still have to exert some force.

-10^2/2(-9.8) +.8

I do not understand how you get this expression or what it means.