/sci/ - Science & Math

also, H obviously stands for height and T obviously stands for time. If that really is obvious I don't know. I'm tired as fuck.

you mean physics test? just take the derivative and set it equal to 0

>>3048043
Okay, I'm probably going to be banned for this but I'm hoping whatever mod or people see this will have compassion and not report/ban me.
I'm underage, this is for a generals math unit test on Quadratics tomorrow. I actually plan on going into engineering so I'm hoping that you guys will actually see I have ambition and don't ban me. If you do at least help me first...

>>3048056
^this post is also me telling you I have no idea what you're talking about.

Uhhhh, bump?

>>3048056
>going into engineering

I was right about to help you too. What a shame.

Surely you can reason it out. What is t equal to when h is 30? What does this represent? How can you apply the quadratic formula from this?

>>3048078
I'm good at math, but not so much science. I planned on going into the Canadian Forces as an Engineer Officer then going into whatever specialized engineering I decided to study afterwards. Please help...

>>3048056
>engineering

Rot in hell faggot!

Solve h=30 for t. You should get two values. large t-small t = time in the air above 30m

For maximum height, I would do derivatives but if you don't have this tool you could probably solve for h=0 for t. Since the median distance between these two is the time at which the parabola is at its maximum...then you take the difference of this divided by 2 and use that value of t for max height.

>>3048056

Engineering

you are the lowest common denominator of the academic world. Enjoy your endless supply of men to fuck you in the ass.

>>3048083
We don't like your kind around here. It's not natural. Stay away from our children!

>>3048091
Not trying to start a bragfest or anything, but my father is a P. Eng and he makes a 6 figure salary, so I don't think that is too shitty.

>>3048089
I'm really brain dead right now, could you possibly do the problem whilst showing the solution, if it's not too much trouble. Thanks.

Okay, so what are all of your professions then?

sorry, engineers dont fucking post their middle school algebra homework on 4chan

>>3048115
Secondary school, but close enough I guess?
This is science and math, I have had fuck all help from google searches so I thought I'd ask science and math...

>>3048123

/sci/ - Science & Math

All science and math related topics welcome.
Homework threads will be deleted, and the poster banned.
No "religion vs. science" threads.

I guess engineers don't know how to math or read.

h = -4.9t^2 +27t +2.4

30 = -4.9t^2 +27t +2.4
-4.9t^2 +27t-27.6=0
therefore t = 1.35, 4.15

I think.

screw this problem, just derive the quadratic formula and youll ace the test.

>>3048110
>>3048110
P. Eng = Phallus engineering = Makes Dildos

>>3048132
Umm the back of the book says 2.8s so I don't think those are right...I was thinking, why don't I get the maximum height (I dont know how to on this problem) then find how long it takes to get to 30m, THEN find the difference between the two and I would have 2.8 seconds.
>>3048133
I have been trying, I get what I'm assuming are the correct zeroes but I don't know where I go from there.

USE DERIVATIVES, JESUS CHRIST OP

>>3048132
so it would be above 30 metres for 4.15-1.35 = 2.8 seconds.

For maximum height, dh/dt = -9.8t+27 = 0
t= 2.755, so h(2.755) = ......

>>3048141
Professional Engineering, He's an electrical engineer, and makes six figures. I don't care about your opinion on engineers. But whatever profession makes that kind of money I daresay it's usually worth it. Unless it's a really shitty job.

>>3048128
>I guess engineers don't know how to math or read

No shit.

>>3048150
My brain is a cloud, someone explain derivatives. Oh cool, triple post.

>>3048153
>Dad literally sucks cock for a living
>Brags that he makes so much money for it

>>3048156
STOP SWALLOWING CUM!

>>3048160
He actually does something to do with SCADA systems. I ain't mad, bro.
>>3048152
Okay, but you just skipped from standard form with the 30 put in to the solutions, could you explain a bit better? haha

>>3048154
I don't get it.

>>3048156

You don't need derivatives. It's calculus. If you haven't learned calculus...

>>3048147
no, no, not use the quadratic formula, actually derive it.

>>3048174
I'm grade 10, I have not learned calculus

>>3048164
which bit don't you get?

>>3048184
What is the solution that you used to get those? you just go from -4.9t^2 +27t-27.6=0
to = 1.35, 4.15

>>3048174

Sorry it's blurry...but note in the picture how the vertex of any parabola will lie right in between two t values. You actually don't even need to solve for t=0. If you used the t values you found for where the height is 30, add them, and divide by 2, you get the same result.

Should be 2.76 actually did some math wrong in there.

>>3048190
use quadratic formula on -4.9t^2 +27t-27.6

>>3048194
>>3048192
Ah, okay, I see. I use the quadratic formula and somehow I get -4.1 AND a -1.35 (weird rounding but ya) whereas both of you seem to get a positive 4.1...

>>3048214

Did you make a on the denominator negative? cause it should be and that will give you an opposite sign.

>>3048225
I have tried the quadratic formula, about a hundred times from 11pm to 1:48am and I NEVER noticed that. I feel fucking retarded

>>3048232
<span class="math"> x= \frac{-b +/- \sqrt{b^2-4ac}}{2a} [/spoiler]

>>3048225
Okay now how do I get the maximum height. Obviously vertex, but I'm REEALLLY brain dead now. Could you just explain this last thing for me?

>>3048239
-b/2a to the time it takes to get there, then sub that answer into the original expression for h

>>3048241
Okay, so my answer matches up with the back of the books but WHY is it -b/2a?

>>3048241
Also, when I complete the square my vertex ends up being 2.75, 61.2 where am I going wrong?

>>3048250
when the derivative(rate at which h is increasing or decreasing)=0,
(derivative h)=0=-2At+B
its calculus, so you dont need to understand it completely

>>3048250
just ignore that! haha I figured it out, i forgot a decimal! Anyways thanks for your help, it was immense

>>3048035


h = -4.9t^2 +27t +2.4

time it's over 30 m implies
30<-4.9t^2 +27t +2.4
subtract 30 from both sides to get
0<-4.9t^2 +27t +2.4-30
Solve for t using the quadratic equation
t = 1.35, 4.15
Since you have a downward opening parabola then between the two points it's greater than that height.
so (1.35,4.15) for that part

To find the maximum use t=-b/(2a) for the time at which you have a maximum and h(-b/(2a)) for the height where you have a maximum.


Good luck on your test.

>>3048257
*should be postive 2At,
so 0=2At+B

find out what the first (lesser) value of t and the second (greater) value of t is for when h = 30.

t2 - t1 = time it was 30m or above

To find out how long it is in the air for 30 minutes, h = 30, solve for t

To find the max height, differentiate with respect to t, set to 0, solve, etc