Physics-Help!

[johnjohn320]

Alright, I understand the bulk of what's going on here, but there's a few steps I'm not so clear on. See if you can help me out...

Two runners are running toward each other with a flagpole between them. Runner A starts initially 4 miles west of the flagpole running 6 m/h east; Runner B initially starts 3 miles east of the flagpole, running 5 m/h west. How far from the flagpole do they meet?

Here's the work I got from the board:

A--> d = (6.0m/h) * t
B--> d = (5.0m/h) * t

total distance = 7 miles

da= 7-db
da= (6.0m/h) * (db/5.0)

7-db = 6 m/h * (db/(5 m/hr)

7-db = 1.2db
7=2.2db
3.18=db

da=7-3.18=3.82

db-(distance from flag) = 3.18 - 3m = 0.18 miles



Ok, I don't understand this step:

da= (6.0m/h) * (db/5.0)

Where did that come from? Why do you multiply runner A's velocity by runner b's distance over velocity?

From there on out, I'm pretty sure I get it all. I just don't understand where that step came into play. Any help?

Thanks!

 

[Chaotic42]

6 meters per hour? Damn that's about how fast I can run.

 

[johnjohn320]

Originally posted by: Chaotic42
6 meters per hour? Damn that's about how fast I can run.

miles

 

[Mayhem1869]

i give up. stupid me fvcked off in H.S. and never took physics. i will regret it forever.

 

[johnjohn320]

Originally posted by: Mayhem1869
i give up. stupid me fvcked off in H.S. and never took physics. i will regret it forever.

Yeah, I've a feeling I'll soon regret taking AP Physics this year. This was assigned the 2nd day of class, I'm supposed to be "reviewing," and I'm already getting lost.

 

[DrPizza]

Two runners are running toward each other with a flagpole between them. Runner A starts initially 4 miles west of the flagpole running 6 m/h east; Runner B initially starts 3 miles east of the flagpole, running 5 m/h west. How far from the flagpole do they meet?

I'm going to assume 6 m/h means miles per hour and not meters per hour....

they start 7 miles apart and are approaching each other at a net rate of 11 miles per hour..
(imagine the road is a conveyor belt... but you get to control the speed.... run the conveyor belt at 4 mph to match runner A's speed, in which case runner B will be moving 11 mph toward runner A. It's all about the frame of reference)

Okay find the time for 7 miles at 11mph

Then, calculate how far either runner runs in that amount of time, then where he'd be in relation to the flagpole.

 

[Mayhem1869]

stick it out man. it's hard to get a second chance after getting married, kids, etc.

 

[johnjohn320]

Originally posted by: DrPizza
Two runners are running toward each other with a flagpole between them. Runner A starts initially 4 miles west of the flagpole running 6 m/h east; Runner B initially starts 3 miles east of the flagpole, running 5 m/h west. How far from the flagpole do they meet?

I'm going to assume 6 m/h means miles per hour and not meters per hour....

they start 7 miles apart and are approaching each other at a net rate of 11 miles per hour..
(imagine the road is a conveyor belt... but you get to control the speed.... run the conveyor belt at 4 mph to match runner A's speed, in which case runner B will be moving 11 mph toward runner A. It's all about the frame of reference)

Okay find the time for 7 miles at 11mph

Then, calculate how far either runner runs in that amount of time, then where he'd be in relation to the flagpole.

I could be mistaken, but this sounds like a COMPLETELY different approach then what I have above...you lost me...

 

[Excelsior]

Hey, I am taking AP Physics also. Which book do you have? The one with the snowboarders on the front? You can PM me anytime if you have a question.

 

[mugs]

They teach that in PHYSICS? That's hardly physics at all... MAYBE if you threw these guys off a building and their initial velocity was 7 mi/h...

DrPizza's answer was right.

 

[Excelsior]

Originally posted by: mugsywwiii
They teach that in PHYSICS? That's hardly physics at all... MAYBE if you threw these guys off a building and their initial velocity was 7 mi/h...

DrPizza's answer was right.

Its the first couple weeks of Physics dude.

 

[mugs]

Originally posted by: Excelsior

Originally posted by: mugsywwiii
They teach that in PHYSICS? That's hardly physics at all... MAYBE if you threw these guys off a building and their initial velocity was 7 mi/h...

DrPizza's answer was right.

Its the first couple weeks of Physics dude.

Then johnjohn is in for a LONG year.

 

[johnjohn320]

Originally posted by: Excelsior
Hey, I am taking AP Physics also. Which book do you have? The one with the snowboarders on the front? You can PM me anytime if you have a question.

I have a question right now...scroll up.


And no, I have the book with the biker on the cover.

 

[johnjohn320]

.

 

[Excelsior]

Originally posted by: johnjohn320

Originally posted by: Excelsior
Hey, I am taking AP Physics also. Which book do you have? The one with the snowboarders on the front? You can PM me anytime if you have a question.

I have a question right now...scroll up.


And no, I have the book with the biker on the cover.

I think DrPizza already helped you out with that one. I wish we had the same book, damn. Anyway..we are doing Kinematics now (vectors, velocity, accelleration, etc).

 

[johnjohn320]

Originally posted by: DrPizza
Two runners are running toward each other with a flagpole between them. Runner A starts initially 4 miles west of the flagpole running 6 m/h east; Runner B initially starts 3 miles east of the flagpole, running 5 m/h west. How far from the flagpole do they meet?

I'm going to assume 6 m/h means miles per hour and not meters per hour....

they start 7 miles apart and are approaching each other at a net rate of 11 miles per hour..
(imagine the road is a conveyor belt... but you get to control the speed.... run the conveyor belt at 4 mph to match runner A's speed, in which case runner B will be moving 11 mph toward runner A. It's all about the frame of reference)

Okay find the time for 7 miles at 11mph

Then, calculate how far either runner runs in that amount of time, then where he'd be in relation to the flagpole.

You're right, that gets the correct answer, too. So what the heck is is all this gibberish I have above? It's all copied directly from my teacher's work on the board.

 

[churchdoesmatter]

good luck with fluid mechanics / thermodynamics in college if you can't even get through PRE-PHYSICS.

 

[johnjohn320]

Originally posted by: pokemonlover
good luck with fluid mechanics / thermodynamics in college if you can't even get through PRE-PHYSICS.

Sigh...thanks for the help.

BTW, this is Physics AP. I got an A in regular physics last year. I'm just rusty.

 

[Chaotic42]

Originally posted by: pokemonlover
good luck with fluid mechanics / thermodynamics in college if you can't even get through PRE-PHYSICS.

Good luck getting into a college if you can't even master 4TH GRADE ENGLISH SKILLS.

 

[johnjohn320]

So, does anyone have any idea how to decipher that step in my teacher's work? Even though DrPizza's way works, I think I'm gonna have to do it my teacher's way to score well on his test.

 

[esun]

Ok, I don't understand this step:

da= (6.0m/h) * (db/5.0)

Where did that come from? Why do you multiply runner A's velocity by runner b's distance over velocity?

Look at these equations:

da = (6.0m/h) * t
db = (5.0m/h) * t

Now if we solve for t in the second equation: t = db/5.0

Now we plug t into the first equation: t = 6.0 * db/5.0

So that's where that step comes in.

 

[johnjohn320]

Originally posted by: esun

Ok, I don't understand this step:

da= (6.0m/h) * (db/5.0)

Where did that come from? Why do you multiply runner A's velocity by runner b's distance over velocity?

Look at these equations:

da = (6.0m/h) * t
db = (5.0m/h) * t

Now if we solve for t in the second equation: t = db/5.0

Now we plug t into the first equation: t = 6.0 * db/5.0

So that's where that step comes in.

*smacks forehead.* Duh, I feel stupid now. Thank you, that's all I needed!

 

[churchdoesmatter]

Originally posted by: Chaotic42

Originally posted by: pokemonlover
good luck with fluid mechanics / thermodynamics in college if you can't even get through PRE-PHYSICS.

Good luck getting into a college if you can't even master 4TH GRADE ENGLISH SKILLS.

i've got a BS/MS in Computer Engineering.

 

[johnjohn320]

Originally posted by: pokemonlover

Originally posted by: Chaotic42

Originally posted by: pokemonlover
good luck with fluid mechanics / thermodynamics in college if you can't even get through PRE-PHYSICS.

Good luck getting into a college if you can't even master 4TH GRADE ENGLISH SKILLS.

i've got a BS/MS in Computer Engineering.

And not a whole lot of people skills... nevermind I'm not gonna get into a pissing match, I got the help I needed. Thanks.