Yet another physics question

[Jeff7]

Yes, this is from homework, no it is no longer worth any points. It's from about a week ago. I know it's probably simple, but I can't figure it out. My Physics textbook's only mention of terminal velocity is to define it as the fastest speed that something can go while falling through a fluid.

The question:

A 220 N bag of nails falls at its terminal
(maximum) speed.
How much air resistance acts on the nails?

Answer in units of N.


There's no mention of the size of this bag. Wouldn't that have an impact? How does one find the terminal velocity of an object?

 

[JMWarren]

None, the air resistance acts on the bag not the nails.

 

[TuxDave]

At terminal velocity there is no more acceleration due to air resistance. So net force on the bag equals zero.

 

[Jeff7]

Originally posted by: TuxDave
At terminal velocity there is no more acceleration due to air resistance. So net force on the bag equals zero.

So the air resistance would be equal to the weight of the nails, 220N in this case?

 

[KingGheedora]

sum of forces = mass x acceleration

Since we know that the bag is falling at its terminal velocity, by definition, it is falling at a constant speed. AKA, it is not accelerating. Thus a = 0. This means "sum of forces" in the equation above is equal to zero.

There are two forces, gravity (-mg), and air resistance (r).

mg = r

I believe mg = 220N
so r = 220N

 

[Jeff7]

Thought so. Really really simple.
I saw the term "terminal velocity" and figured something like, "need coefficient of friction of air, need to know speed of nails, need to know size of bag, but question doesn't give any of this, I must be missing something really goddamn obvious."

 

[iamaelephant]

resistance = 220 * 9.8ms^-2 isn't it?

 

[Mo0o]

Originally posted by: iamaelephant
resistance = 220 * 9.8ms^-2 isn't it?

why would you multiply the force by acceleration again?

 

[iamaelephant]

Originally posted by: Mo0o

Originally posted by: iamaelephant
resistance = 220 * 9.8ms^-2 isn't it?

why would you multiply the force by acceleration again?

I don't know, I'm hungover

 

[Born2bwire]

Originally posted by: iamaelephant

Originally posted by: Mo0o

Originally posted by: iamaelephant
resistance = 220 * 9.8ms^-2 isn't it?

why would you multiply the force by acceleration again?

I don't know, I'm hungover

Friends don't let friends drink and derive.

 

[Billzie7718]

Originally posted by: Born2bwire

Originally posted by: iamaelephant

Originally posted by: Mo0o

Originally posted by: iamaelephant
resistance = 220 * 9.8ms^-2 isn't it?

why would you multiply the force by acceleration again?

I don't know, I'm hungover

Friends don't let friends drink and derive.

Hehe. That made me giggle.