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Yet another physics question

Jeff7

Jeff7

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

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