# Finding the difference in range of a projectile (air resistance vs. free)

• Aug 22nd 2012, 04:46 PM
Shakespoe
Finding the difference in range of a projectile (air resistance vs. free)
We were give two equations that show the position as a function of time on the x and y axis where there is a linear drag force of 'beta*a vector v'. I have already solved for the case of no air resistance. The following are the two equations which include air resistance:
x(t) = x(t=0) + ((m*vo(x))/beta)*(1-e^((-beta/m)*t))
--> x(t=0) is 0, giving:

x(t) = [(m*vo(x))/beta]*[1-e^((-beta/m)*t)]

y(t) = [(vo(y)*(m/beta))+g*((m/beta)^2)]*[1-e^((-beta/m)*t)]-(g*(m/beta)*t)
--> y(t) would be 0, considering the full path of the trajectory results in no delta y, so setting the equation equal to 0, I was able to start solving for 't' to plug into the equation for x(t) to find a total Range.

However, I am caught on the exponential function since it includes 't'. I am not sure how to get that out of there so I can solve for 't' without including 't' in the result. This is where I am so far:

t = [(vo(y)+m)/g*beta]*[beta*(1-e^((-beta/m)*t))]

If you all could help me, I would greatly appreciate it! I'm sorry if there is a way to input equations, I am new to the forum and don't know how to do that if there is a way.

Thanks everyone!
-Tina
• Aug 23rd 2012, 10:51 PM
MaxJasper
Re: Finding the difference in range of a projectile (air resistance vs. free)
You don't need to eliminate t in order to find a single function of y=f(x), but rather you have x(t) and y(t) as two parametric functions which define your projectile and you can plot it too.

It means you vary t and calculate x(t) & y(t) that give your projectile.

Assuming:
m=10
v0x=1
v0y=10
beta=3
g=9.8

Trajectory would look like:

http://mathhelpforum.com/attachment....1&d=1345793283