# Modeling with Differential Equations

## Homework Statement

A falling body of mass m, encounters air resistance proportional to its instantaneous velocity, v. Use Newton's second law to find the DE for the velocity, v at time, t.

## Homework Equations

I've been reading this section quite a bit and am still not getting it! I'd appreciate a simple breakdown of this problem.

## The Attempt at a Solution

I know Newton's second law is F=ma, and a=$\frac{dv}{dt}$= -g, in this problem. I've checked the answer in the back of the book to see if I can work it backwards and then maybe get an idea of whats going on, but I don't think I've dealt with air resistance, k, in any problems before. Even in my physics class.

SammyS
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## Homework Statement

A falling body of mass m, encounters air resistance proportional to its instantaneous velocity, v. Use Newton's second law to find the DE for the velocity, v at time, t.

## Homework Equations

I've been reading this section quite a bit and am still not getting it! I'd appreciate a simple breakdown of this problem.

## The Attempt at a Solution

I know Newton's second law is F=ma, and a=$\frac{dv}{dt}$= -g, in this problem. I've checked the answer in the back of the book to see if I can work it backwards and then maybe get an idea of whats going on, but I don't think I've dealt with air resistance, k, in any problems before. Even in my physics class.
Newton's 2nd Law: The net force on a body of mass, m, is given by Fnet = ma .

For this problem Fnet = mg - kv , and is in the downward direction.

Newton's 2nd Law: The net force on a body of mass, m, is given by Fnet = ma .

For this problem Fnet = mg - kv , and is in the downward direction.

I see. There was an image next to the question with those being opposite. Now to put ity into a differential equation form? I was watching a video about differential equations and there being a 1st ODE format using p(x) and q(x)?

haruspex