Yes, heroin is derived from poppys, but a wholly different type from the poppys from which we get the little edible seeds. The problem with the drug test is that is does not test for the chemicals that are the "drug" part of the plant (that part which causes a change in human physiology). It tests for other chemicals in poppys that are longer-lasting, therefore making it possible to "catch" drug users several days after they took the drug last.

Unfortunately, both legal poppys and illegal poppys have the same general chemicals.

Thanks Lil Dog Turpy for providing the equation. There is an additional aspect of Terminal Velocity - the top speed an object can reach owing to mass versus surface area versus air density (which relates to friction).