Jumping out a plane force of wind resistance

[physicsgurl12]

Homework Statement

If you jumped out of a plane you would begin speeding up as you fall downward. eventually due to wind resistance your velocity would become constant with time. after this occurs the magnitude of the force of wind resistance is
a. slightly smaller than the force of gravity acting on you
b. equal to the force of gravity
c. greater than the force of gravity

Homework Equations

g=v/t

The Attempt at a Solution

slightly smaller?

 

[hotvette]

slightly smaller?

Why would that be?

 

[physicsgurl12]

honestly, I am not really sure
but i think it would be because the only two forces are gravity and air resistance and air restiance would cause it to be slighty smaller

 

[lightgrav]

It's true that air resistance would never get "quite" as strong as gravity, so you would continue to gain speed (slightly) till you hit ground.
BUT
The question is about AFTER "your velocity becomes constant" .
IF your velocity is constant, what about those two Forces?

 

[physicsgurl12]

if your velocity is constant your not accelerating

 

[lightgrav]

your acceleration is zero. (we like zero's).
so the Forces?

 

[physicsgurl12]

if acceleration is zero the force would be zero?

 

[lightgrav]

which is zero?
gravity? wind resistance? the difference? the sum? the average? ...

 

[physicsgurl12]

um. you kinda lost me there. gravitys not zero ever? and i wouldn't think wind resistance could be. the average of what?

 

[lightgrav]

you said "the force would be zero" ... as if there was only one possible choice.

 

[physicsgurl12]

well if f=ma and if a=0 then f=0

 

[lightgrav]

have you not yet seen Σ ? it is the ΣF = ma

 

[physicsgurl12]

i have, but i don't remeber what it means

 

[physicsgurl12]

all forces acting on an object?
would the answer be equal to gravity?

 

[lightgrav]

it means "Sum" ... as in "it is the Sum of Forces that cause a mass to accelerate".

You add the constant gravity Force vector (which direction?)
to the increasing air resistance Force vector (which direction?)
to get the mass to accelerate with a getting smaller and smaller (downward) till zero.

 

[physicsgurl12]

gravity vector is down air resistance is up.
so the answer is b?

 

[lightgrav]

yes. (after you've achieved "approximately constant velocity" = terminal speed)

 

[physicsgurl12]

sweet thanks

 

[lightgrav]

yes (after reaching "terminal speed" = approximate constant velocity)