Surface area

[rain charm]

Anyone able to help with this been stuck on it for a while?

[dusty ridge]

well the length of the cylinder is 51cm
both of the semi-spheres are going to 85-51 which is 34cm

so both semi-spheres have a radius of 34cm

oops i guess i mean hemisphere

[rain charm]

Why would it be 85-51 to find the radius of the hemispheres?

[dusty ridge]

so surface area of a cylinder is 2πr² + 2πrh
(2π34²) + (2π(34)(51))
= 18,158.4cm²
surface area of the 2 hemispheres
2(3πr²)
= 2(3π34²)
= 21,790.8cm²

[dusty ridge]

because the total length of the hemispheres and the cylinder combined is 85cm while the cylinder's length is 51cm so taking 51 away from 85 gives us the hemispheres radius'

[rain charm]

Ah ok

[dusty ridge]

now the final answer is
21,790.8 + 18,158.4 = 39,949.2cm²

[rain charm]

I see, what equation did you use to find the SA of the cylinder again?

[dusty ridge]

i dont think i've done these equations in school yet but it seems easy enough to do so i looked them up and the cylinder surface area equation seemed to be 2πr² + 2πrh

[rain charm]

Fair enough lol, lemme just re-answer it now and see if it’s right

[dusty ridge]

okay

[rain charm]

Is this to 1dp already?

Just making sure

[dusty ridge]

yes

39,949(.2)

⭐

[rain charm]

Idk if I just typed it wrong or if the answer was incorrect but it saying it was wrong

[dusty ridge]

gasp

[rain charm]

Fr lol

Should I send u a new ss of it now?

[dusty ridge]

ok

[rain charm]

Just incase it’s diff

Just same steps I’m assuming

[dusty ridge]

😭 why does it change

that weird

yeah

[rain charm]

Idk lol

[dusty ridge]

but

i'm weirded out by the cylinder surface area

[rain charm]

The equation of it?

[dusty ridge]

you've already found the area of the two circles so why is there a 2πrh

is it not just 2πr²h

okay hold on

[rain charm]

Yea on the vid the equation is 2 X pi X r X h

For the cylinder

[dusty ridge]

hemisphere radius: 77-35 = 42cm

2(3πr²)
2(3π42²)
= 33,250.6cm²

2πr²h
2π42²(35)
= 387,923.9cm²

= 387,923.9 + 33,250.6 = 421,174.5cm²

try that

[rain charm]

Alrighty fingers crossed

[dusty ridge]

🤞

[rain charm]

Bro that still didn’t work

I’m being dead serious rn

[dusty ridge]

😭

hm

oh i might know

we're finding the 2 circles surface areas with the hemisphere surface area thing and the cylinder

so really it's just 2(3πr²)h i think

maybe

i'm not sure

[rain charm]

Hm let’s see

[dusty ridge]

there's a bunch of new equations in this that i haven't really learnt lol

what are you guys learning in y10 😭

[rain charm]

Idk man this is new to me aswell

[dusty ridge]

😭

[rain charm]

Dk why this is my hw lol

[dusty ridge]

hm

new image since it changes

[rain charm]

Changes every 2 times I get wrong

It’s the same rn

[dusty ridge]

ah

okay... so...
2 x 3πr² + h (here's hoping tbh)
2 x 3(1794π) + 35
= 33,851.1cm²
please tell me if it's correct ::((

😭

😭

i beg

[rain charm]

Third times a charm they say

Let’s see

[dusty ridge]

lmao

[rain charm]

BRO WTH

[dusty ridge]

hm?

[rain charm]

I’m actually fed up of this now

Wrong

[dusty ridge]

BRUH

i'm gonna jump no i wont do that

[rain charm]

Lol

Dw il ask my teacher on monday

Let’s not stress bout this

[dusty ridge]

😦

hold on

maybe if i draw it out it'll help

[rain charm]

Hm try it

[dusty ridge]

for visualisation

did it change

[rain charm]

Or

I could screen record the video they give for the question

And see if it helps maybe

[dusty ridge]

hm

if the question changed can i get a pic

[rain charm]

Here’s the vid

Il send new question

[dusty ridge]

YOU HAVE TO FIND THE CURVED SURFACE AREA??

[dusty ridge]

i didn't know that

[rain charm]

Which parts the curved sa?

I’m still lost lol

[dusty ridge]

hemisphere

and cylinder

surface area of cylinder and hemisphere and curved surface area of cylinder and hemisphere

hold on

okay i think i got it

r = 79 - 45 = 34cm

2πrh
2 x π x 34 x 35
= 2380π

hold on

not done

2(2πr²)
2(2 x π x 34²)
= 4624π

7004π
= 22,003.7cm²

praying

[rain charm]

Please love of god

Be correct

BRO NAH THATS INCORRECT

[dusty ridge]

Jeopardy:
When some gets something right on a maths question, what might a teacher yell out?
(beep) What is correct?
Correct!

SHIT

the thing is

they make it so problem solving for you

since the video only contains one hemisphere

[rain charm]

Yea ik

[dusty ridge]

but the question contains 2

[rain charm]

The vids don’t help

Ngl

[dusty ridge]

which might make it harder to calculate how much hemisphere you need since they also seem to half the surface area of a sphere

[rain charm]

Na let’s not worry about this anymore tbh

[dusty ridge]

which just becomes 2 x pi x r^2

[rain charm]

Il ask my teacher dw

U tried to help a lot

[dusty ridge]

😦

[rain charm]

U been trying for an hour

Just forget it dw

[dusty ridge]

nuh uh

[rain charm]

Hm u don’t give up

@dusty ridge I gotta go to my boxing training rn tho, so if u do find another answer just ping me in it and I can respond in about an hour and a half from now

But u don’t have to still

[dusty ridge]

ok

[rain charm]

Alr cya when I get back

[dusty ridge]

@rain charm 345,009.7cm²

lets see when u get back

[charred crypt]

The reason it wasn't working is because you are calculating the surface area of the full cylinder, you only need to calculate the curved surface of the cylinder, not the two circular faces as well

[dusty ridge]

ik

which i think i haven't done now

have my fingers crossed

[charred crypt]

Also, minusing the one length from the other gives you the diameter not the radius

@dusty ridge @rain charm

[dusty ridge]

it isn't the diameter

see where it's located

if it was the diameter it'd go across the hemisphere area

but it's at the top so it's the height of the cylinder

[charred crypt]

What you yapping

minusing the length of a cylinder plus two hemispheres from the length of a cylinder just gives you the two hemisphere radii which is the diameter

[dusty ridge]

yeah but you need to find the two hemisphere surface area and curved surface areas separately

[charred crypt]

why

[dusty ridge]

halving the radius mean you've just halved the radius of the hemisphere

and in that video since the hemisphere is basically have of 4xpixr^2

it's just 2xpixr^2

[charred crypt]

the radius of a hemisphere is the same as the radius of a sphere you know

[dusty ridge]

i know?

[charred crypt]

79 take 45 gives you the diameter

[charred crypt]

yes which is multiplied by 2 to account for both hemispheres

[dusty ridge]

they're already hemispheres so you've already found the radius of them because from a 3D viewpoint, the line that is 34cm spins around and stays the same in the hemisphere

so the diameter would be 68

radius is 34

[charred crypt]

bro you're killing me

[dusty ridge]

mhm

[charred crypt]

let me load up paint

[dusty ridge]

yes but you have to find the surface area of the circles on the cylinder and the curved surface areas

actually no

💀 are you serious

if you do 79-45, it makes 34 on each hemisphere

leading to the hemisphere's radius' being 34cm

not 17

[charred crypt]

is this some sort of joke

jus6t look at the paint diagram

its proof is definitive

[dusty ridge]

okay honestly i'm confused bye bye

[charred crypt]

becuase you have been disproven 💀

[dusty ridge]

nah

[charred crypt]

moral of the story, dont try and help unless you know yourself what is going on

[dusty ridge]

you're just saying to boost some sort of ego tbh

[dusty ridge]

actually, it's better to help than to just ignore, because you may be the only person to help 😊

[charred crypt]

if the help is wrong then its not help

[dusty ridge]

if one of the hemispheres has a radius of 34, so does the other one because they're both identical, so the diameter added up would be 68

79 - 45 = 34, which accounts for at least one of the hemispheres, since they're both the same they both have a radius of 34

[charred crypt]

but you only minus the cylinder length from the whole length so you get what is left which is 2 hemispheres which is just a sphere

[charred crypt]

it accounts for exactly two

[dusty ridge]

yeah i realise that now 😭

[charred crypt]

at least you know now

[dusty ridge]

yes

@rain charm so basically look at the calculations made but replace the 34 with 17 and yeah

[dusty ridge]

or this

[rain charm]

Yo I’m back

@dusty ridge @charred crypt what’s this about with it being 17 not 34?

Fill me in

[charred crypt]

Essentially, because you are given the length of the whole thing then just the length of the cylinder, minusing the cylider from the whole thing gives you 2 hemisphere radii which means you need to divide by 2 to give the the single radius

[rain charm]

So because theirs 2 hemispheres, you have to split the 34 equally to get the individual radius’s which is 17 for each??

[dusty ridge]

Yes

Since if you relocate the 45 to the end/start point of the 75 cm line, it makes the length of the two circles at the end

(Ik I didn’t do this but) or using knowledge, add up the two lines to give you 34 and then half it for the 2 hemispheres

Although 34 is the answer for both lines added up I guess

[rain charm]

Oh I see, also I used ur calculations and subbed 17 into it and I got it right now!

It was worth it in the end lol

[charred crypt]

👏

[dusty ridge]

Hooray

[rain charm]

Thank you guys for the help, anyways ima make this solved now lol