# Math problem :P

#### galaxyAbstractor

Community Support
An oildrop with the volume 0.1 cubiccentimetres spread across the water making a 40 squaremetre large circular area with the same thickness. How thick is the layer of oil?

Lol just want to see how many gets the right answer :biggrin:

#### Mitch

##### New Member
Is it 0.000025 squaremetre?

#### galaxyAbstractor

Community Support

#### vievie

##### Member
My answer is 0.00000025m in thickness. Assuming the layer of oil is a cylinderical shape =P

BTW, remember conversion of cm^2 to m^2 is not a factor of 100, but 10000

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#### kirtik

##### New Member
Lol? I just did this the other day in my A level Physics class.

The layer is one molecule of oil thick.

4/3 Pi R^3 = sphere
Pi r^2 h = cylinder

Due to the conservation of volume rule,

4/3 Pi R^2 = Pi r^2 h

Rearrange formula to get:

h= (4/3 Pi R^3) / (Pi r^2)

Substitute known values...

0.1 cc = 1.0 x 10^-7 m^3

40m^2 = Pi r^2

Therefore, h = (1 x 10^-7) / (40)

h = 0.0000000175m.

#### leafypiggy

##### Manager of Pens and Office Supplies
Staff member
i think that h = 1.39299399492883848939949939 where the 39299399492883848939949939 repeats. JK. lol. I'm only in algebra 1. lol'

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#### Mitch

##### New Member
um you are the right way
Yeah.

Try this:

y=ax+b+c

Calculate a, b and c.

Use this: y=a(x+p) ²+q
Top of the parabola (0, 5). I goes the point: (5, 3)

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#### kirtik

##### New Member
Is it 0.000025 squaremetre?
? How can a height be in square metres?

#### galaxyAbstractor

Community Support
My answer is 0.00000025m in thickness. Assuming the layer of oil is a cylinderical shape =P

BTW, remember conversion of cm^2 to m^2 is not a factor of 100, but 10000

Right!

Took me 15 minutes to figure out and I did forgot some things so here is how I did (I bet it isn't the best way):

40/3.14 = 12.73.
*sqr*12.73 = 3.57.

The radious of the circle is 3.57 Metres.

3.57 Metres = 357 Centimetres

357^2*3.14 = 400 000 squarecentimeters

400 000 * 0.00000025 = 0.1 cubiccentimetres

Thickness 0.00000025 cubiccentimetres = 2.5 * 10^-9