SOLUTION: Water flows through a circular pipe of internal diameter 3cm at a speed of 10cm/sec. If the pipe is full, how much water flows from the pipe in one minute? (answer in litres)

If the pipe is long enough, then in 1 minute a given drop of water
water will move  through the pipe.
Let's pretend that instead of the water flowing out of the pipe, onto
the ground or into a vat, that instead we attach another circular 
pipe onto the end of the the given pipe.  Pretend this attached pipe 
is exactly 600cm long and has the same 3 cm internal diameter as the given pipe. 

Instead of the water flowing out of the given pipe onto the ground or 
into a vat, we think of the water just exactly filling this new pipe we 
imagine to have been placed at the end. It would then fill this new 
attached pipe in exactly one minute.  And the amount of water in this 
imagined attached pipe after one minuter would be the same as the amount 
of water that would flow out of the pipe onto the ground or into a vat 
in one minute.

So we need to find the volume of this imagined 600cm long pipe with
 3 cm diameter.  We use the formula for a cylinder:



Since the diameter is 3 cm, the radius R is 1.5 cm.



Since a cubic centimeter and a milliliter are the same quantity, the

volume is .  We convert milliliters to liters
by moving the decimal 3 places left.  So the final answer is

liters, or about liters.

Edwin