# Estimating error using differentials

• Mar 20th 2007, 07:36 PM
camherokid
Estimating error using differentials
Use differential to estimate the amount of paint needed to apply a coat of paint 0.05cm thick to a hemispherical dome with diameter 50cm.

S= 2 pi r^2

ds= 4 pi r dr.

r= 50/2= 25 cm

dr= 0.05cm

So ds= 4 pi 25*0.05= 5 pi cm^2
• Mar 20th 2007, 07:44 PM
Jhevon
Quote:

Originally Posted by camherokid
Use differential to estimate the amount of paint needed to apply a coat of paint 0.05cm thick to a hemispherical dome with diameter 50cm.

S= 2 pi r^2

ds= 4 pi r dr.

r= 50/2= 25 cm

dr= 0.05cm

So ds= 4 pi 25*0.05= 5 pi cm^2

i may be wrong, but isn't the amount of paint talking about volume?
• Mar 20th 2007, 07:53 PM
camherokid
So the answer must be this :

V= 2/3* pi r^3

dV= 2 pi r^2 dr.

r= 50/2= 25 cm

dr= 0.05cm

So dV= 2 pi 25^2*0.05= 62.5 pi cm^3
• Mar 20th 2007, 08:08 PM
Jhevon
Quote:

Originally Posted by camherokid
So the answer must be this :

V= 2/3* pi r^3

dV= 2 pi r^2 dr.

r= 50/2= 25 cm

dr= 0.05cm

So dV= 2 pi 25^2*0.05= 62.5 pi cm^3