Yeah, it's yet another one of those "3 people" jokes

from my friend John
 

A chemist, a physicist, and an economist are stranded on a desert island with nothing to eat.

After several days a can of beans washes ashore, and the three academics apply their disciplines to the problem of opening the can.

The physicist offers the first solution: "Raise the can and let it drop.  Its potential energy will be converted into kinetic energy according to mgh = (mv^2)/2, and for sufficiently large h this energy upon impact will be enough to breach the can."

The chemist replies "That's all very well, but we have no means to raise the can much higher than our heads.  Besides, there is a simpler way.  Build a fire and place the can in it.  The volume of the can being fixed, the pressure in the can will increase according to Boyle's Law, PV = nRT, until it is large enough to breach the can."

The economist replies, "But that would scatter the beans all over the sandy beach.  Besides, we have no means to build a fire.  Besides, there is a simpler way.  Assume we have a can opener... "