Velocity from a force time graph

[TheFluffyDuck]

Homework Statement

The figure is a graph of the force exerted by the floor on a woman making a vertical jump.
At what speed does she leave the ground? Hint: The force of the floor is not the only force acting on the woman.

Homework Equations

The Attempt at a Solution

I am completely lost with this question. First I derived her mass from the 600N from the graph. Which was about 61.22kg

Then I calculated the Impusle from the area underthe graph, but where from? All the area or minus the forces of gravity? then I used:

Impulse= m(delta v)

But I am not getting anywhere :(

 

[Astronuc]

Starting with this: Impulse= m(delta v)

Then delta v = Impulse/m, and delta v = v - v_o, and v_o = ?

 

[TheFluffyDuck]

Im guessing Vo is zero becasue she is jumping straight up?

Do I calculate Impulse to be the entire area under the graph or just a certain segment under the graph?

 

[Astronuc]

Im guessing Vo is zero becasue she is jumping straight up?

Correct. Standing she starts are rest.

Do I calculate Impulse to be the entire area under the graph or just a certain segment under the graph?

Weight which is a force, does not provide for acceleration. One has to consider the force in excess of the weight.

 

[TheFluffyDuck]

Correct. Standing she starts are rest.



Weight which is a force, does not provide for acceleration. One has to consider the force in excess of the weight.

Thanks for your replies.
So since F=mg, and I derived mass from 600/9.8. does that mean that the impusle is the area of the graph from anything that is >600n?

 

[Astronuc]

Thanks for your replies.
So since F=mg, and I derived mass from 600/9.8. does that mean that the impusle is the area of the graph from anything that is >600n?

The 600 N is her weight, when she is not moving, so the force in excess of 600 N goes toward accelerating her mass.

 

[Astronuc]

Another way of looking at this problem is to convert F(t) to a(t), since a(t) is just F(t)/m, however, one has to look at F_net(t), which is the difference between F_total(t) and mg.