GS-2 Physical Sciences Question 33

[aref.qu6209]

I was going to pick C for an answer but thought that increasing temperature can decrease density (Answer D). What do u think?

[mcat_premed3832]

It is very important to review Archimedes' Principle because if "fluids" is mentioned on your upcoming MCAT, then this would be tested quite commonly.

Archimedes Principle states that the buoyant force on a submerged object is equal to the weight of the fluid that is displaced by the object. What is the downward force of the buoyant object? It's weight NOT density.

So your suggestion that, for example, a temperature increase would reduce density (of course - for a piece of wood - you're right but we are talking about a relatively very very very small density change) is true. But less density means more volume but the mass and therefore the weight is the same. The shape of the buoyant object is not relevant: if the weight is unchanged then it has to less nor any greater force to push aside the surrounding water.