volumes help (1 Viewer)

[john-doe]

i know how to calculate volumes when solids are revolved around the x and y axis..but how can u translate it when the axis of rotation is not one of them eg y=2, x= -2 blah blah...do u add or subtract??

also can they ask to find volume when the solid is revolved around an axis that is not parallel to x or y axis eg calculate volume when (this curve) is rotated about y=x-5! ?????

 

[john-doe]

bump

 

[Carrotsticks]

Think of it as a distance, rather than just blindly adding or subtracting. But usually it's subtracting.

So for example if you want to find the distance between x (assume positive) and -5, then the distance is x - (-5) = x+5.

Also, rotations done around a non-vertical or horizontal axis is the same as usual except you use Pythagoras' Theorem for the thickness dx or dy (kinda like component forces for vectors)

 

[john-doe]

Also, rotations done around a non-vertical or horizontal axis is the same as usual except you use Pythagoras' Theorem for the thickness dx or dy (kinda like component forces for vectors)

can it be in exam, there arent any questions of that type in sk patel textbook?

 

[Carrotsticks]

Not that I know of in Patel. The only book that I know, which covers rotation around y=mx+b, is the Cambridge 4U textbook.

Highly doubt it will be in your HSC, or Trials, unless your school does the Cambridge textbook.