[ARCHIVED THREAD] - Science riddle: (Page 1 of 3)
Posted: 9/10/2013 4:25:24 AM EDT
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You're in a row boat along with a steel anchor. The row boat is in a swimming pool. You throw the anchor out which sinks completely and rests on the bottom of the pool with slack in the rope up to the boat.
Does the water level in the pool rise, fall or stay the same? 
PS: List your reasoning. |
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The water displaced is identical whether the rope and anchor are in the boat or in the water. No change in depth. Aw, AeroE, I'm disappointed. The displacement is different. The anchor displaces its weight while in the boat. It only displaces its volume while resting on the bottom. The water level will drop. |
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The water displaced is identical whether the rope and anchor are in the boat or in the water. No change in depth. I thought it was equal displacement of weight, not volume. As such, wouldn't the level of the water fall as the weight of the anchor is now resting on the bottom of the pool, and not displacing water when it's on board? (yes, I realize a volume of water equal to that of the anchor volume would be displaced, but it wouldn't equal the weight displacement it generated on the boat) ETA: thread is moving quickly, I see my point has already been brought up. |
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Aw, AeroE, I'm disappointed. The displacement is different. The anchor displaces its weight while in the boat. It only displaces its volume while resting on the bottom. The water level will drop. Quoted:
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The water displaced is identical whether the rope and anchor are in the boat or in the water. No change in depth. Aw, AeroE, I'm disappointed. The displacement is different. The anchor displaces its weight while in the boat. It only displaces its volume while resting on the bottom. The water level will drop. ahhhhh soooooo.... learned something before breakfast!! Thanks! (now my brain hurts....) |
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I love problems like this. Anybody got any more.
This question was supposedly on a Tesla employment interview application. I DID come up with the answer on my own. Another was: How many ways can you think of to move water from the lake at the base of a mountain to the top? I'm still compiling a list. I'm down to about number 20: trebuchet heaving water balloons. 
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The water was already displaced because the anchor was in shared mass of the boat. Quoted:
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you introduced volume to the column of fluid, displacing it a like volume. yes, it rises. (what do I win?) The water was already displaced because the anchor was in shared mass of the boat. This is the correct answer but did it occur to any of you that this boat may be filled with firearms and is on the verge of a tragic boating accident. |
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I thought it was equal displacement of weight, not volume. As such, wouldn't the level of the water fall as the weight of the anchor is now resting on the bottom of the pool, and not displacing water when it's on board? (yes, I realize a volume of water equal to that of the anchor volume would be displaced, but it wouldn't equal the weight displacement it generated on the boat) ETA: thread is moving quickly, I see my point has already been brought up. Quoted:
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The water displaced is identical whether the rope and anchor are in the boat or in the water. No change in depth. I thought it was equal displacement of weight, not volume. As such, wouldn't the level of the water fall as the weight of the anchor is now resting on the bottom of the pool, and not displacing water when it's on board? (yes, I realize a volume of water equal to that of the anchor volume would be displaced, but it wouldn't equal the weight displacement it generated on the boat) ETA: thread is moving quickly, I see my point has already been brought up. Hollow anchor! That's correct. When the rope and anchor are in the boat the displaced volume is greater than when the anchor is in the water. Ridgerunner9876 is a tricky guy and I'll be watching him closer now! |
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The anchor cracks the concrete on the bottom of the pool causing a leak which cools the core of the earth. This causes a reduction in CO2 emissions by the earth, resulting in a dramatic temperature rise. This temperature rise loosens the lug nuts on Subnets Miata to a point where he is able to change his wheels out in around 15 minutes.
The boat operator dies, just because. |
| Goes down slightly. When it's in the boat, it dispaces its weight in water, causing the water level in the pool to rise. When it's dropped into the pool it displaces only its volume in water. Since it's specific weight is higher than the surrounding water, it displaces less water while in the pool than when it's buoyed up in the boat. |
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CHANGE UP: Now, the anchor DOES NOT reach the bottom. What happens to the water level? Nothing. It's still buoyed up by the same volume of water. edited to respond to opinions below: the volume of the chain/anchor is irrelevant. When the anchor is danging in the water, it does displace its volume in water but because of that, there's less force on the anchor chain, so the boat displaces less water to hold the anchor up. End result: no change in water level. |
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up marginally (anchor and submerged chain volume). Quoted:
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CHANGE UP: Now, the anchor DOES NOT reach the bottom. What happens to the water level? up marginally (anchor and submerged chain volume). Let's see what others say before I give my opinion. |
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The level falls. Originally enough water was displaced to float the anchor. Now less is displaced. Because the density of the anchor is more than water. Originally the volume of water displaced is equal to the water density times the weight of the anchor. After the anchor is dropped, the displacement is equal to the density of the anchor times the weight of the anchor (ie the volume of the anchor) Volume of anchor < water density times weight of anchor |
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Rises Because the weight is still on the boat so its displacement hasn't decreased plus you now have the water being displaced by the volume of the anchor. Quoted:
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CHANGE UP: Now, the anchor DOES NOT reach the bottom. What happens to the water level? Rises Because the weight is still on the boat so its displacement hasn't decreased plus you now have the water being displaced by the volume of the anchor. This. The anchor is displacing more water because of a higher specific gravity. It would displace the difference between its volume and it's SG and the level would rise by that much.. |
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This. The anchor is displacing more water because of a higher specific gravity. It would displace the difference between its volume and it's SG and the level would rise by that much.. Quoted:
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CHANGE UP: Now, the anchor DOES NOT reach the bottom. What happens to the water level? Rises Because the weight is still on the boat so its displacement hasn't decreased plus you now have the water being displaced by the volume of the anchor. This. The anchor is displacing more water because of a higher specific gravity. It would displace the difference between its volume and it's SG and the level would rise by that much.. See my post above. The water level doesn't change. edited to add: You bought the false premise that "its weight is still on the boat," which is wrong. When you dip an anchor in the water, the tension on the anchor chain is slightly less than the anchor's full weight because the anchor is displacing water. |
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Water level drops. Weight displaces more water through the hull of the boat than the volume of the anchor itself. Where's my monkey? You might want to rethink that "I want a monkey" thing. 
http://www.ar15.com/forums/t_1_5/1530533_Monkey_attacks_8mo_baby_and_eats_his_testicle.html |
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See my post above. The water level doesn't change. edited to add: You bought the false premise that "its weight is still on the boat," which is wrong. When you dip an anchor in the water, the tension on the anchor chain is slightly less than the anchor's full weight because the anchor is displacing water. Quoted:
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CHANGE UP: Now, the anchor DOES NOT reach the bottom. What happens to the water level? Rises Because the weight is still on the boat so its displacement hasn't decreased plus you now have the water being displaced by the volume of the anchor. This. The anchor is displacing more water because of a higher specific gravity. It would displace the difference between its volume and it's SG and the level would rise by that much.. See my post above. The water level doesn't change. edited to add: You bought the false premise that "its weight is still on the boat," which is wrong. When you dip an anchor in the water, the tension on the anchor chain is slightly less than the anchor's full weight because the anchor is displacing water. On second go-round, I'm thinking this is correct. You're losing the displacement for the boat by the SG equal to the volume of the anchor and the anchor is displacing that volume by being in the water. I agree. Hanging anchor from the boat = zero water level change. That was more difficult than the grounded anchor. |
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Easy, The water level goes down. The anchor is denser than water and initially displacing an equal mass of water = volume greater than the steel anchor. After the anchor goes into the water it is only displacing an equal volume of water = volume equal to steel anchor and less displacement of water. Now I'll read to see if I missed something... |
