The thickness of a hollow wooden cylinder is $2 \mathrm{cm}.$ It is $35 \mathrm{cm}$ long and its inner radius is $12 \mathrm{cm}.$ Find the volume of the wood required to make the cylinder, assuming it is open on either end.

How many cubic metres of earth must be dug out to sink a well $22.5 \mathrm{m}$ deep and of diameter $7 \mathrm{m} ?$

A hollow cylindrical pipe is $21$ dm long. Its outer and inner diameters are $10$ cm and $6$ cm, respectively. Find the volume of the copper used in making the pipe.