Forces on a Skydiver during the initial frefall phase of the jump

[Balsam]

Homework Statement

A skydiver is jumping out of an airplane. During the first few seconds of one jump, the parachute is unopened, and the magnitude of the air resistance acting on the skydiver is 251N. The acceleration of the skydiver during this time is 5.96 m/s^2 [down]. Calculate the mass of the skydiver.
g=9.8 m/s^2[down]
air resistance=251N[up]
acceleration=5.96m/s^2 [down]

Homework Equations

Fnet=ma
Fg=mg

The Attempt at a Solution

[/B]
I drew a diagram and have plugged in the known variables to each equation. For Fg=mg-- Fg=m(9.8m/s^2[down])

for F=ma-- Fnet=m(5.96 m/s^2[down]).

for Fnet--Fnet= 251N[up] + m(9.8 m/s^2 [down]) x 5.96 m/s^2[down].

I'm stuck here, I don't know how to solve for mass from here.

 

[SteamKing]

Homework Statement

A skydiver is jumping out of an airplane. During the first few seconds of one jump, the parachute is unopened, and the magnitude of the air resistance acting on the skydiver is 251N. The acceleration of the skydiver during this time is 5.96 m/s^2 [down]. Calculate the mass of the skydiver.
g=9.8 m/s^2[down]
air resistance=251N[up]
acceleration=5.96m/s^2 [down]

Homework Equations

Fnet=ma
Fg=mg

The Attempt at a Solution

I drew a diagram and have plugged in the known variables to each equation. For Fg=mg-- Fg=m(9.8m/s^2[down])

for F=ma-- Fnet=m(5.96 m/s^2[down]).[/B]

for Fnet--Fnet= 251N[up] + m(9.8 m/s^2 [down]) x 5.96 m/s^2[down].

I'm stuck here, I don't know how to solve for mass from here.

You should draw a free body diagram of the skydiver and label the forces acting on his body while he's falling. Then, write your equation for Fnet.

 

[Balsam]

You should draw a free body diagram of the skydiver and label the forces acting on his body while he's falling. Then, write your equation for Fnet.

I did. I assume the only forces are air resistance and gravity and i came to the conclusion that Fg must be greater than 251N (in terms of magnitude) for the person to be falling.

 

[SteamKing]

I did. I assume the only forces are air resistance and gravity and i came to the conclusion that Fg must be greater than 251N (in terms of magnitude) for the person to be falling.

The way you wrote the equation for Fnet in the OP is confusing. Try expressing Fnet in terms of the weight of the skydiver and the drag force. Don't include the net acceleration just yet.

 

[kmpellin]

Fnet=251N-mg=ma
251N=ma+mg
251N=m(a+g)
251N=m(-5.96m/s/s+9.8m/s/s)
251N=m(3.89m/s/s)
251N/(3.89m/s/s)=m
65.36kg=m