Physics help.

2008-09-20 12:46:32

#1

Whiplash: Future Aviator; +40|6236|Central Texas

A student wanted to drive from Austin to
San Antonio, 80 miles south of Austin on
highway I35. Unfortunately, he entered the
highway in the wrong direction and drove all
the way toWaco — 100 miles north of Austin
— before he noticed his error. In Waco,
he turned around, drove back to Austin and
continued to San Antonio. The whole trip
took 6.74 hours.
What was the student’s average speed dur-
ing this trip? Answer in units of MPH.

011 (part 2 of 2) 10.0 points
What was the student’s average velocity dur-
ing his trip? Take your positive direction to
be southbound on I35. Answer in units of
MPH.

Ok, for the answer to number 11 I got 26.70623145, but it says that it's wrong. What am I doing wrong?

2008-09-20 12:48:41

#2

TrueMusou: Member; +36|6616|United States Of Hamerica

41.54 mph

Edit: You add 100mi to 180mi. Then divide the sum by 6.74 hours. No biggy.

Last edited by TrueMusou (2008-09-20 12:50:32)

2008-09-20 12:51:56

#3

Jenspm: penis; +1,716|7187|St. Andrews / Oslo

I'm guessing you didn't multiply 100miles with 2 (we drove back and forth)

https://static.bf2s.com/files/user/26774/flickricon.png

2008-09-20 12:52:33

#4

Whiplash: Future Aviator; +40|6236|Central Texas

It says that's wrong too. I'm doing this online. Velocity is in a certain direction so shouldn't it be only 180 miles?

2008-09-20 12:56:31

#5

TrueMusou: Member; +36|6616|United States Of Hamerica

Whiplash wrote:
It says that's wrong too. I'm doing this online. Velocity is in a certain direction so shouldn't it be only 180 miles?

Oh velocity.

Well then you'd have to figure out how long it took it to go North. Then neglect the time it took to go north (wrong direction) from the total time in your final calculation. So you then can use 180mi. However, I don't know how to figure that out at the moment. Good luck.

2008-09-20 12:56:59

#6

Jenspm: penis; +1,716|7187|St. Andrews / Oslo

I'm assuming they want you do record the 100miles in the wrong direction as a deceleration I guess.

which would be retarded, but w/e.

2008-09-20 12:57:46

#7

Scorpion0x17: can detect anyone's visible post count...; +691|7221|Cambridge (UK)

try 11.86943620178041543026706231454

2008-09-20 12:58:23

#8

Whiplash: Future Aviator; +40|6236|Central Texas

Ugh, I've gotten the answer wrong 3 times. This is stupid.

2008-09-20 13:00:19

#9

Whiplash: Future Aviator; +40|6236|Central Texas

Scorpion0x17 wrote:
try 11.86943620178041543026706231454

How'd you get that?

2008-09-20 13:01:09

#10

Scorpion0x17: can detect anyone's visible post count...; +691|7221|Cambridge (UK)

Whiplash wrote:
Scorpion0x17 wrote:
try 11.86943620178041543026706231454
How'd you get that?

Is it correct?

2008-09-20 13:01:43

#11

Jenspm: penis; +1,716|7187|St. Andrews / Oslo

is 11.87mph the correct answer?

edit - Scorpion beat me.

V=distance/time
V=180-100/time
V=80/time

Last edited by Jenspm (2008-09-20 13:02:54)

2008-09-20 13:02:21

#12

Whiplash: Future Aviator; +40|6236|Central Texas

Yea, it's correct. I wanna to know how you got it though so I know what I was doing wrong.

Ahh, I kept trying to do 180 and 280. Didn't even try 80, but I see how that makes sense. Stupid me =P

Last edited by Whiplash (2008-09-20 13:04:15)

2008-09-20 13:03:45

#13

Scorpion0x17: can detect anyone's visible post count...; +691|7221|Cambridge (UK)

You ignore the distance part of the whole of the trip to Waco and back, but not the time - just divide the distance from Austin to San Antonio by the TOTAL time taken for the whole trip.

Last edited by Scorpion0x17 (2008-09-20 13:05:03)

2008-09-20 13:03:57

#14

Jenspm: penis; +1,716|7187|St. Andrews / Oslo

Whiplash wrote:
Yea, it's correct. I wanna to know how you got it though so I know what I was doing wrong.

positive direction: 180 miles
negative direction: 100 miles

therefore, postive distance covered is 80miles, divide that by the time and you have the velocity.

2008-09-20 13:05:34

#15

Whiplash: Future Aviator; +40|6236|Central Texas

Thanks for the help guys, I understand now.

2008-09-20 13:06:16

#16

Scorpion0x17: can detect anyone's visible post count...; +691|7221|Cambridge (UK)

What age are you Whiplash? (what level physics is this?)

2008-09-20 13:06:46

#17

Jenspm: penis; +1,716|7187|St. Andrews / Oslo

That task was retarded.

Trying to put physics into those kind of real life situations ftl.

2008-09-20 13:07:47

#18

Defiance: Member; +438|7126

Whiplash wrote:
Thanks for the help guys, I understand now.

If it was asking for speed, which is not a vector and has no direction, then 100+180 would be right. Since it's velocity, and velocity is a vector, it's just displacement/time.

Just because no one said it explicitly.

2008-09-20 13:08:04

#19

Whiplash: Future Aviator; +40|6236|Central Texas

I'm only 16, this is my first year in physics. School just started like 4 weeks ago. This is introductory stuff, but I was just getting confused a little bit.

2008-09-20 13:08:43

#20

Scorpion0x17: can detect anyone's visible post count...; +691|7221|Cambridge (UK)

Jenspm wrote:
That task was retarded.

Trying to put physics into those kind of real life situations ftl.

That's why I'm wondering what level it's at...

2008-09-20 13:09:48

#21

Scorpion0x17: can detect anyone's visible post count...; +691|7221|Cambridge (UK)

Whiplash wrote:
I'm only 16, this is my first year in physics. School just started like 4 weeks ago. This is introductory stuff, but I was just getting confused a little bit.

Right, cool. At that level, just remember that most of it is basic algebra.

2008-09-20 13:09:59

#22

Defiance: Member; +438|7126

Scorpion0x17 wrote:
That's why I'm wondering what level it's at...

Basic kinematics... word problems... first year.

2008-09-20 13:12:25

#23

liquidat0r: wtf.; +2,223|7082|UK

Jenspm wrote:
Trying to put physics into those kind of real life situations ftl.

That's what Physics is, no? At least in kinematics, anyway. It's applying maths to solve problems identical to these ...

2008-09-20 13:14:00

#24

Jenspm: penis; +1,716|7187|St. Andrews / Oslo

liquidat0r wrote:
Jenspm wrote:
Trying to put physics into those kind of real life situations ftl.
That's what Physics is, no? At least in kinematics, anyway. It's applying maths to solve problems identical to these ...

who tries to find the average possitive velocity when driving a car?

Average speed, sure.

2008-09-20 13:25:52

#25

liquidat0r: wtf.; +2,223|7082|UK

Fair enough. I was treating your statement as a generalization, which it was.

BF2S Forums Physics help.

Whiplash wrote:

Scorpion0x17 wrote:

Whiplash wrote:

Scorpion0x17 wrote:

Whiplash wrote:

Whiplash wrote:

Jenspm wrote:

Whiplash wrote:

Scorpion0x17 wrote:

Jenspm wrote:

liquidat0r wrote:

Jenspm wrote:

Board footer