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pls help if you're good at maths!

does anyone understand this question and could possibly help?
it is:
'a sphere and a cylinder have equal volumes.
the sphere has radius 3r. the cylinder has radius 2r and height h.
find h in terms of r'.

i'm so confused could someone possibly attempt to explain it?
Formulas we need:
Volume of sphere of radius r =43πr3 = \frac{4}{3} \pi r^3
Volume of cylinder of radius r and height h =πr2h = \pi r^2 h



Volume of sphere of radius 3r =43π(3r)3=43π27r3=36πr3 = \frac{4}{3} \pi (3r)^3 = \frac{4}{3} \pi 27r^3 = 36 \pi r^3
Volume of cylinder of radius 2r and height h =π(2r)2h=4πr2h = \pi (2r)^2 h = 4 \pi r^2 h

We are given that these volumes are equal so 36πr3=4πr2h36 \pi r^3 = 4 \pi r^2 h and so h=9rh=9r.
(edited 7 years ago)
Original post by sophie7194
does anyone understand this question and could possibly help?
it is:
'a sphere and a cylinder have equal volumes.
the sphere has radius 3r. the cylinder has radius 2r and height h.
find h in terms of r'.

i'm so confused could someone possibly attempt to explain it?


You know the formulae for the volumes

Vsphere=43πr3V_{sphere} = \frac{4}{3} \pi r^3
Vcylinder=πr2hV_{cylinder} = \pi r^2 h

the question has stated that they are equal so we set Vcylinder=VsphereV_{cylinder}=V_{sphere}

we then just rearrange to make it in the form h=stuffh=stuff
1)Use Vol of sphere formula and plug in r = 3r
2)Use Vol of cylinder formula and plug r =2r
3)After finding their volumes' in terms of h and r in steps one and two, equate them together as their volumes are equal
4) Once you equate them together you can work with the equation till you set it equal to h.
Reply 4
Original post by Leicester City
You absolute dumb ****. Use the formulae pages in your paper! They're practically giving you the answers you dumbo.


chill out lol
Reply 5
Original post by Leicester City
You absolute dumb ****. Use the formulae pages in your paper! They're practically giving you the answers you dumbo.


We should really make downvotes a thing on this forum...
Reply 6
Original post by Leicester City
You absolute dumb ****. Use the formulae pages in your paper! They're practically giving you the answers you dumbo.



We should really make downvotes a thing on this forum...
Original post by leicester city
you absolute dumb ****. Use the formulae pages in your paper! They're practically giving you the answers you dumbo.



i'm going to cry laugh when u post a thread tomorrow about ur paper having a manufacturing problem and they missed out the formula page and no one helped you.

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