1, rotating with the width as the axis, that is, with the length as the bottom radius, its volume is:

3. 14× 12? ×5=2260.8(cm？ )

2, cutting into a cylinder, there are three cutting methods:

1) With the surface composed of length and width as the bottom surface, the maximum diameter is 2.5dm, the height is 3dm, and the volume is (2.5/2)? π×3=4.6875π;

2) With the surface composed of width and height as the bottom surface, the maximum diameter is 2.5dm, the height is 3dm, and the volume is (2.5/2)? π×3=6.25π

3) The surface consisting of length and height is the bottom surface, with the maximum diameter of 3dm, the height of 2.5dm and the volume of (3/2)? π×2.5=5.625π

In the second case, the volume is the largest, and the volume of the cylinder is 6.25 π = 19.625 cubic decimeter.