Not Your Usual Cylinder - Volume

Geometry Level 3

Given the following information, find the volume of the oblique cylinder shown above:

  • The flat sides of the cylinder are circular, congruent and parallel to each other.
  • The slant height of the cylinder is l = 5. l = 5.
  • The radius of the circular base is r = 2. r = 2 .
  • The perpendicular height of the cylinder is h = 4. h = 4.
  • The image is not drawn to scale.

State your answer to five significant figures.


Also try: Not Your Usual Cylinder - Surface Area


The answer is 50.265.

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2 solutions

Pranshu Gaba
Jan 13, 2016

If you take a rectangle and displace one of its sides parallel to the other side the area of the shape does not change. All the parallelograms thus formed have the same base length, the same perpendicular height and therefore have the same area. This is a 2-dimensional example of Cavalieri's principle .

Similarly, if you take a right cylinder and displace one of its flat faces parallel to the other flat face, then you obtain an oblique cylinder with the same volume as the original right cylinder. This is a 3-dimensional example of Cavalieri's principle .

The right cylinder will have the same perpendicular height as the oblique cylinder, h = 4 h = 4 . The radius of the circular base will be r = 2 r =2 . Therefore the volume of the right cylinder, and also the volume of the oblique cylinder is π × r 2 × h = π × 2 2 × 4 = 16 π 50.265 \pi \times r^{2} \times h = \pi \times 2^{2} \times 4 = 16 \pi \approx \boxed{ 50.265} _\square


You can also check out this interactive Math Open Reference link where you can adjust the height, radius, and the slant height of the cylinder and observe how the volume changes. (Click 'options' in lower right corner to 'allow oblique' and 'freeze height'.)

Moderator note:

Similarly, the volume of a pyramid with a fixed base depends only on the height of the apex, and is independent of it's x-y location. This is why we learn the pyramid volume formula as 1 3 A h \frac{1}{3} Ah .

Atul Shivam
Jan 13, 2016

as per the given figure volume of oblique cylinder is equal to π × r 2 × l π×r^2×l s i n θ sin \theta where s i n θ sin \theta is the angle formed between l l & r r

so volume is equal to π × 4 × 5 × 4 5 π×4×5×\frac{4}{5} which comes up to be 50.265 \boxed {50.265} .

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