The Student Room Group

Help with pressure in fluids question

This is a question from an OCR A-level physics "modelling physics" practice paper, the answer is C - 0.6, but i don't know how to get to the answer. Any help is appreciated! :smile:question.png
(edited 6 years ago)
Original post by puPper
...


Define the unknown volume of the cylinder as VV and the submerged volume as a constant multiplied by VV e.g. kVkV.

You can use Archimedes' principle which states that the mass of the object is equal to the mass of the displaced fluid (submerged volume of the object multiplied by the density of the fluid).

Form an equation and solve for kk to obtain the fraction of the cylinder's volume which is submerged.

Your expression should end up as a ratio of the two densities:

k=ρwoodρwaterk = \dfrac{\rho_{\text{wood}}}{\rho_{\text{water}}}.
(edited 6 years ago)
Reply 2
Screen Shot 2017-06-13 at 11.13.28.png
due to Archimedes' principle: (upthrust experienced by wood) = (weight of water displaced)

therefore: (density of wood)*A*L = (density of water)*A*x

therefore: x/L = (density of wood)/(density of water) = (6x10^2)/(1x10^3) = 0.6
Reply 3
Original post by milkm4n
Screen Shot 2017-06-13 at 11.13.28.png
due to Archimedes' principle: (upthrust experienced by wood) = (weight of water displaced)

therefore: (density of wood)*A*L = (density of water)*A*x

therefore: x/L = (density of wood)/(density of water) = (6x10^2)/(1x10^3) = 0.6

Thank you so much for this explanation, it helped a lot! :smile:
Reply 4
Original post by pleasedtobeatyou
Define the unknown volume of the cylinder as VV and the submerged volume as a constant multiplied by VV e.g. kVkV.

You can use Archimedes' principle which states that the mass of the object is equal to the mass of the displaced fluid (submerged volume of the object multiplied by the density of the fluid).

Form an equation and solve for kk to obtain the fraction of the cylinder's volume which is submerged.

Your expression should end up as a ratio of the two densities:

k=ρwoodρwaterk = \dfrac{\rho_{\text{wood}}}{\rho_{\text{water}}}.


Thank you! This helps a lot! :smile:

Quick Reply