You are sitting in a boat on a lake, you have with you in the boat a large rock. You throw the rock out of the boat and it sinks to the bottom of the lake, does the water level of the lake go up, down or stay the same?
Whilst in the boat the rock (and you) are floating, this means that the amount of water displaced by the rock is the mass of the rock. When the rock sinks to the bottom of the lake the amount of water displaced by the rock is the volume of the rock.
As the rock sinks to the bottom of the lake, we know that the rock is more dense than water.
As the rock is more dense than water, the rock will displace more (a greater volume of) water when floating than when at the bottom of the lake. This means that after throwing the rock out of the boat the water level of the lake as a whole will go down.
JB
Related Physics A Level answers
All answers ▸A ball is thrown in the air with velocity of 50.0 m/s, assuming no air resistance calculate its maximum height.
A guitar string 0.65m long vibrates with a first harmonic frequency of 280Hz. Mary measures 1m of the string and discovers that it weighs 8.0x10^-4 kg. What is the tension in the guitar string?
How does the photoelectric effect actually show that light is made up of particles?
A light wave has a wavelength of 420nm, calculate the energy of this wave in joules.