Posers and Puzzles

Posers and Puzzles

  1. Joined
    31 May '06
    Moves
    30743
    27 Jun '06 22:01
    Two men put a large rock into a rowing boat & take it to the middle of a large pond. They then throw it over the side.
    How does the water level change?
  2. Earth Prime
    Joined
    16 Mar '05
    Moves
    21936
    27 Jun '06 22:07
    My 8th grade science teacher tried to tell us that when you sink something it water, it will displace the weight of water equal to it's weight. She was wrong. This displacement rule only comes into effect if something is floating.

    The water will not rise the moment the rock is dropped. It rose when the boat, rock, and men entered the lake, and will sink again when the men and boat exit the lake. The rock's displacement will remain, as it is now at the bottom of the lake. No level will change at the moment the rock is removed from boat and placed in lake.
  3. Joined
    31 May '06
    Moves
    30743
    27 Jun '06 22:09
    close, but no cigar
  4. Joined
    12 Mar '03
    Moves
    37826
    27 Jun '06 22:19
    While in the boat, the rock displaces a volume of water that has the same weight as the rock. Once in the water, the rock only displaces water equal to its volume, which is less (assuming the 'rock actually' sinks, of course). Hence, when the rock is in the water, the water level will be lower (less upwards displacement).
  5. Earth Prime
    Joined
    16 Mar '05
    Moves
    21936
    27 Jun '06 23:00
    Originally posted by Mephisto2
    While in the boat, the rock displaces a volume of water that has the same weight as the rock. Once in the water, the rock only displaces water equal to its volume, which is less (assuming the 'rock actually' sinks, of course). Hence, when the rock is in the water, the water level will be lower (less upwards displacement).
    OH. right. I answered it in my first part sorta, then went on to claim the wrong answer.
  6. Joined
    20 Feb '06
    Moves
    8407
    28 Jun '06 10:56
    Originally posted by Mephisto2
    While in the boat, the rock displaces a volume of water that has the same weight as the rock. Once in the water, the rock only displaces water equal to its volume, which is less (assuming the 'rock actually' sinks, of course). Hence, when the rock is in the water, the water level will be lower (less upwards displacement).
    This is correct. Imagine you had a grain of sand in the boat that weighed 100kg. In the boat it really pushes the boat down (and hence water up) whereas on the bottom of the pond its effect is negligible.
  7. Joined
    12 Mar '03
    Moves
    37826
    28 Jun '06 11:02
    Originally posted by SPMars
    This is correct. Imagine you had a grain of sand in the boat that weighed 100kg. In the boat it really pushes the boat down (and hence water up) whereas on the bottom of the pond its effect is negligible.
    Alien sand?
  8. Earth Prime
    Joined
    16 Mar '05
    Moves
    21936
    28 Jun '06 21:39
    Originally posted by SPMars
    This is correct. Imagine you had a grain of sand in the boat that weighed 100kg. In the boat it really pushes the boat down (and hence water up) whereas on the bottom of the pond its effect is negligible.
    actually I think it would be quite likely to cut through the boat before you got it out there, being so much mass on such a consentrated point. 😛
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