## Math help plox

• 1,408 Views
• 35 Replies
kiljoy96
kiljoy96
• Member since: Jul. 2, 2008
• Offline.
Forum Stats
Member
Level 21
Musician
Math help plox 2011-06-17 03:18:46

I'm completely stumped on how to do this.
Basically, I'm in the very early research stages of a project. I've been doing physics and trig for the past 2 hours, and I just can't remember how to make an exponential graph, or even find out what I'm trying to find out.
At an acceleration rate of 229^2 inches a second, how much distance is covered between the dead stop and hitting 60 miles an hour? Is it just simply the acceleration rate multiplied by the time taken or something?

SteamID: Fetus

redfield95
redfield95
• Member since: Jun. 23, 2008
• Offline.
Forum Stats
Member
Level 08
Art Lover
Response to Math help plox 2011-06-17 05:18:16

Divide by zero :3

Sobolev
Sobolev
• Member since: Mar. 14, 2004
• Offline.
Forum Stats
Member
Level 44
Melancholy
Response to Math help plox 2011-06-17 05:31:14

basic answer: consider the equation v^2-u^2=2as and plug in the numbers.

advanced answer: even though the space-time is assumed to be flat, not enough information is given. you did not state whether the velocity and accleartion is with respect to the inertia frame or not.

tox
tox
• Member since: Mar. 13, 2007
• Offline.
Forum Stats
Supporter
Level 28
Audiophile
Response to Math help plox 2011-06-17 05:35:51

At 6/17/11 05:31 AM, i-am-ghey wrote: basic answer: consider the equation v^2-u^2=2as and plug in the numbers.

advanced answer: even though the space-time is assumed to be flat, not enough information is given. you did not state whether the velocity and accleartion is with respect to the inertia frame or not.

Im a firing my ........ o.o......
....... ~ blinks a few times~
...... ~ walked out of the room and closes the door~

call me toxie 0.~

redfield95
redfield95
• Member since: Jun. 23, 2008
• Offline.
Forum Stats
Member
Level 08
Art Lover
Response to Math help plox 2011-06-17 05:40:49

At 6/17/11 05:39 AM, MrPercie wrote: I worked it out to be 16600.87 seconds, anyone else?

Sobolev
Sobolev
• Member since: Mar. 14, 2004
• Offline.
Forum Stats
Member
Level 44
Melancholy
Response to Math help plox 2011-06-17 06:04:53

GiantDouche
GiantDouche
• Member since: Feb. 27, 2005
• Offline.
Forum Stats
Member
Level 19
Blank Slate
Response to Math help plox 2011-06-17 06:16:44

At 6/17/11 06:11 AM, MrPercie wrote: what does u, s and a mean?

USA

Sobolev
Sobolev
• Member since: Mar. 14, 2004
• Offline.
Forum Stats
Member
Level 44
Melancholy
Response to Math help plox 2011-06-17 06:19:15

U is initial velocity
v is final velocity which is zero
s is displacement

they are standard notations in physics you should know it

GiantDouche
GiantDouche
• Member since: Feb. 27, 2005
• Offline.
Forum Stats
Member
Level 19
Blank Slate
Response to Math help plox 2011-06-17 06:29:56

At 6/17/11 06:22 AM, MrPercie wrote: I did know V was velocity though.

LOOKS LIKE WE GOT OURSELVES A MOTHERFUCKIN' PHYSICIST

VitaminP
VitaminP
• Member since: Jun. 4, 2007
• Offline.
Forum Stats
Member
Level 21
Blank Slate
Response to Math help plox 2011-06-17 06:30:45

Also remember to convert your values into the same units i.e using miles and hours for all values or using inches and seconds for all values.

--------------------[ Mod Type Indicator ] - [ Change Level Icons ] - [ Last Post Link ] - [ Inline Poster ]------------------

Gimmick
Gimmick
• Member since: Aug. 20, 2008
• Offline.
Forum Stats
Member
Level 27
Programmer
Response to Math help plox 2011-06-17 07:58:21

At 6/17/11 06:11 AM, MrPercie wrote: what does u, s and a mean?

USA

Slint approves of me! | "This is Newgrounds.com, not Disney.com" - WadeFulp
"Sit look rub panda" - Alan Davies

Ninjafap
Ninjafap
• Member since: Jan. 13, 2011
• Offline.
Forum Stats
Member
Level 01
Blank Slate
Response to Math help plox 2011-06-17 09:10:48

Acceleration is constant. a(t) = a

The integral of acceleration is velocity (acceleration is the change in velocity). v(t) = a t

The integral of velocity is position (velocity is the change in position). p(t) = .5*a*t^2

Substitute velocity in for time. We get: p(t) = .5*a*(v^2/a^2) = .5*(229^2)*(63360^2/299^4) = 22452 inches. Convert it to 1.61 km which you should be using since this is physics.

If you want make a position versus time graph simply plug in your calculator y = .5*(229^2)*t^2 and stop it when time hits (63360^2/299^4) = .502 seconds.

Oh and take calculus. It's fun.

Take my love, take my land. Take me where I cannot stand.

Ninjafap
Ninjafap
• Member since: Jan. 13, 2011
• Offline.
Forum Stats
Member
Level 01
Blank Slate
Response to Math help plox 2011-06-17 09:21:40

What kind of trig were you trying to do and how do you know physics yet alone had this assigned if the position-velocity-acceleration relationship is one of the first things explained in any physics class (even if it's not justified with calculus)? Why did you type this out on Newgrounds instead of making a simple Google search?

Take my love, take my land. Take me where I cannot stand.

Sobolev
Sobolev
• Member since: Mar. 14, 2004
• Offline.
Forum Stats
Member
Level 44
Melancholy
Response to Math help plox 2011-06-17 09:36:50

um... accuracy might be a problem if calculations involve many steps.

it is unnecessary to take a long winded approach to solve this problem. one simple formula that any physics students are expected to know is sufficient.

of course, you can always consider partial derivatives to estimate the value if you don't have a calculator at hand. otherwise, i don't know why you should need to plot a graph at all.

LostFaceInTrain
LostFaceInTrain
• Member since: May. 11, 2011
• Offline.
Forum Stats
Member
Level 03
Blank Slate
Response to Math help plox 2011-06-17 09:38:13

Y'all gay here

___________________________________

Ninjafap
Ninjafap
• Member since: Jan. 13, 2011
• Offline.
Forum Stats
Member
Level 01
Blank Slate
Response to Math help plox 2011-06-17 09:45:06

At 6/17/11 09:36 AM, i-am-ghey wrote: um... accuracy might be a problem if calculations involve many steps.

You're thinking of precision. And no, this is really just a one step plug-and-chug once you derive (or look up) the formula relating position to acceleration.

it is unnecessary to take a long winded approach to solve this problem. one simple formula that any physics students are expected to know is sufficient.

Exactly. I don't know if any one in this thread has taken physics, really.

of course, you can always consider partial derivatives to estimate the value if you don't have a calculator at hand.

There is only a single variable, time, so you can't take partial derivatives.

otherwise, i don't know why you should need to plot a graph at all.

I suppose it's to show how the position changes between the velocities of zero and sixty miles per hour.

Take my love, take my land. Take me where I cannot stand.

Sobolev
Sobolev
• Member since: Mar. 14, 2004
• Offline.
Forum Stats
Member
Level 44
Melancholy
Response to Math help plox 2011-06-17 09:48:26

there is a trick here.

s=u^2/2a, so in fact there are two variables.

you can take differential ds and consider small changes in u and a.

Ninjafap
Ninjafap
• Member since: Jan. 13, 2011
• Offline.
Forum Stats
Member
Level 01
Blank Slate
Response to Math help plox 2011-06-17 09:56:30

At 6/17/11 09:48 AM, i-am-ghey wrote: there is a trick here.

s=u^2/2a, so in fact there are two variables.

you can take differential ds and consider small changes in u and a.

The final velocity isn't zero. Read his post again.

There aren't two variables because we know the acceleration. I suppose he's trying to make position the function of time, not velocity.

Take my love, take my land. Take me where I cannot stand.

Sobolev
Sobolev
• Member since: Mar. 14, 2004
• Offline.
Forum Stats
Member
Level 44
Melancholy
Response to Math help plox 2011-06-17 09:59:17

i supposed you haven't learnt this math tools yet. estimating the value of s is NOT about physics really.

i am a math and physics major.

also, i believe dead stop means 0 velocity.

Sobolev
Sobolev
• Member since: Mar. 14, 2004
• Offline.
Forum Stats
Member
Level 44
Melancholy
Response to Math help plox 2011-06-17 10:00:25

ok. he means 0 to 60.

but the magnitude won't change by symmetry.

JaY11
JaY11
• Member since: Aug. 25, 2005
• Offline.
Forum Stats
Member
Level 21
Melancholy
Response to Math help plox 2011-06-17 10:03:22

Inches and miles per hour? Please tell me physics in the US is not based around the imperial system?

Elfer
Elfer
• Member since: Jan. 21, 2001
• Offline.
Forum Stats
Member
Level 38
Blank Slate
Response to Math help plox 2011-06-17 10:12:41

Oh my fuck, you people need to stop dicking around and just answer his question.

KNOWN:
a = 229 in/s^2 (I'm assuming this is what you meant, because I don't know how acceleration in square inches works in reality)
v0 = 0 in/s
v1 = 60 m/h = 1056 in/s (ffffffffffFFFFFFFFUCK IMPERIAL UNITS)

UNKNOWN:
t1 (time to reach 60 mph)
D (distance covered between t0 = 0 and t1)

INITIAL CONDITIONS:
at t = 0, v = 0 and D = 0

DO SOME MATH:
a = 229 in/s^2
integrate w.r.t. time to find:
v = 229t in/s
and again:
D = (229/2)t^2 in
(both integration constants are zero due to the initial conditions, trivial calculations omitted)

Solve t1:
1056 in/s = 229(t1) in/s
t1 = 4.6114 s

solve D:
D = (229/2)(4.6114^2) = 2434.84 inches
= 202.9 feet
= 0.0384 miles

For fuck's sake

At 6/17/11 10:03 AM, JaY11 wrote: Inches and miles per hour? Please tell me physics in the US is not based around the imperial system?

Prepare to have your mind blown: Many engineers in the real world have to work around imperial units simply because a lot of instruments are designed or manufactured in the US.

Sobolev
Sobolev
• Member since: Mar. 14, 2004
• Offline.
Forum Stats
Member
Level 44
Melancholy
Response to Math help plox 2011-06-17 10:13:51

so no one knows the magic formula v^2-u^=2as?

unbelievable.

Elfer
Elfer
• Member since: Jan. 21, 2001
• Offline.
Forum Stats
Member
Level 38
Blank Slate
Response to Math help plox 2011-06-17 10:19:00

At 6/17/11 10:13 AM, i-am-ghey wrote: so no one knows the magic formula v^2-u^=2as?

unbelievable.

Why memorize formulas when you can derive everything with the power of CALCULUS

Also that formula is meaningless because you don't identify the variables. Convention is not the same everywhere!

JaY11
JaY11
• Member since: Aug. 25, 2005
• Offline.
Forum Stats
Member
Level 21
Melancholy
Response to Math help plox 2011-06-17 10:22:03

At 6/17/11 10:19 AM, Elfer wrote:
Also that formula is meaningless because you don't identify the variables. Convention is not the same everywhere!

V=Final velocity, U=Initial velocity, a=acceleration, s=displacement

I always learned it as V^2=U^2 + 2as though. I might have had a shot at it if I could be bothered googling how to convert miles into inches etc

Sobolev
Sobolev
• Member since: Mar. 14, 2004
• Offline.
Forum Stats
Member
Level 44
Melancholy
Response to Math help plox 2011-06-17 10:33:18

you might be able to derive anything from scratch in elementary physics. but i am trained to use formulae whenever i can (do not require much memory) in both secondary and tertiary education, unless the question specify otherwise.

in fact, it is impossible to not rely on previous results at university level so, it is a good practice to remember these basic formula.

questioning a physics major about standard physics notation? ROFL
Ninjafap
Ninjafap
• Member since: Jan. 13, 2011
• Offline.
Forum Stats
Member
Level 01
Blank Slate
Response to Math help plox 2011-06-17 10:33:30

At 6/17/11 10:12 AM, Elfer wrote: v1 = 60 m/h = 1056 in/s (ffffffffffFFFFFFFFUCK IMPERIAL UNITS)

Oops messed up the conversion there.

Take my love, take my land. Take me where I cannot stand.

Elfer
Elfer
• Member since: Jan. 21, 2001
• Offline.
Forum Stats
Member
Level 38
Blank Slate
Response to Math help plox 2011-06-17 10:34:20

Well okay, then that's just equating the ones I found for velocity and acceleration, i.e.

v = u + at
v^2 = u^2 + a^2t^2
D = (1/2)at^2

I could have gone that route but it's more roundabout and provides less information (i.e. you just equate for time instead of solving for it)

Elfer
Elfer
• Member since: Jan. 21, 2001
• Offline.
Forum Stats
Member
Level 38
Blank Slate
Response to Math help plox 2011-06-17 10:35:05

At 6/17/11 10:33 AM, Ninjafap wrote:
At 6/17/11 10:12 AM, Elfer wrote: v1 = 60 m/h = 1056 in/s (ffffffffffFFFFFFFFUCK IMPERIAL UNITS)
Oops messed up the conversion there.

o rly? What do you get for the conversion?

Ninjafap
Ninjafap
• Member since: Jan. 13, 2011
• Offline.
Forum Stats
Member
Level 01
Blank Slate
Response to Math help plox 2011-06-17 10:47:44

At 6/17/11 10:35 AM, Elfer wrote:
At 6/17/11 10:33 AM, Ninjafap wrote:
At 6/17/11 10:12 AM, Elfer wrote: v1 = 60 m/h = 1056 in/s (ffffffffffFFFFFFFFUCK IMPERIAL UNITS)
Oops messed up the conversion there.
o rly? What do you get for the conversion?

63360 in/s. I converted hours to minutes instead of seconds.

Take my love, take my land. Take me where I cannot stand.