# Homework Help: Velocity of airplanes

1. Dec 2, 2009

### thovia

1. The problem statement, all variables and given/known data
Two airplanes leave Dallas at the same time and fly in opposite directions. one plane flies 80mph faster than the other. After three hours, they are 2940 miles apart. What is the velocity of each plane?

2. Relevant equations
I don't know what equation to use!

3. The attempt at a solution

2. Dec 2, 2009

### xcvxcvvc

Re: velocity

you should use velocity * time = distance

To lessen your confusion on how to use this equation, just pretend you have one plane going as fast as both planes together that travels a total of 2940 miles in three hours.

3. Dec 2, 2009

### thovia

Re: velocity

Thank you soooooooooo much! I never learned how to solve this kind of problem and I'm afraid my physics teacher will eat me if I ask.

4. Dec 2, 2009

### xcvxcvvc

Re: velocity

No problem. Just make sure if you use v(total) * t = d and solve for v(total) that you then set v(total) [the thing we just solved for] equal to x + (x + 80) where x would represent the slower plane's speed. Alternatively, you could use that substitution in the first equation like so: (x + (x + 80)) * t = d ---> (2x + 80) * t = d. When you solve for x, you again get the speed of the slower plane. Adding 80, of course, then gives you the faster plane's speed.

I didn't want to spell it out like this before, because it's against the rules to supply solutions. People are just supposed to guide users.