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Hard question

A piece of ice floats in a glass filled with water. The ice contains a small stone, so that when the ice has all melted, the stone sinks to the bottom of the glass. What will happen to the level of the water in the glass, firstly as the ice melts, and secondly as the stone is released from the ice and sinks to the bottom? The water in the glass will
A. remain the same then rise
B. rise and fall
C. fall then remain the same
D. remain the same then fall

The answer is C but why?
Original post by haron1
A piece of ice floats in a glass filled with water. The ice contains a small stone, so that when the ice has all melted, the stone sinks to the bottom of the glass. What will happen to the level of the water in the glass, firstly as the ice melts, and secondly as the stone is released from the ice and sinks to the bottom? The water in the glass will
A. remain the same then rise
B. rise and fall
C. fall then remain the same
D. remain the same then fall

The answer is C but why?


Surely the ice floating on the water will displace a certain amount of water equivalent to the amount of ice displacing the water. At this point (when the ice hasn't melted yet), the level of water has already increased compared to when the ice is removed from the water. As a result, there is room for the level of the water to be decreased but because the ice is melted while in the water there will not be any decrease in the level of water, as the volume of the water displaced will be occupied as the ice melts until that volume is totally occupied. When the ice has melted completely, more amount of water is added to the water plus the volume of the stone that sinks, increasing the level of the water. So I don't see why the answer would be C when, in fact, it would be A.
Original post by Mehrdad jafari
Surely the ice floating on the water will displace a certain amount of water equivalent to the amount of ice displacing the water. At this point (when the ice hasn't melted yet), the level of water has already increased compared to when the ice is removed from the water. As a result, there is room for the level of the water to be decreased but because the ice is melted while in the water there will not be any decrease in the level of water, as the volume of the water displaced will be occupied as the ice melts until that volume is totally occupied. When the ice has melted completely, more amount of water is added to the water plus the volume of the stone that sinks, increasing the level of the water. So I don't see why the answer would be C when, in fact, it would be A.


Ice takes up 33% more space than water due to its molecular arrangement. It would fall as the ice melts as this space will have been filled up again- at least that's the only explanation I can think of


Posted from TSR Mobile
Original post by haron1
A piece of ice floats in a glass filled with water. The ice contains a small stone, so that when the ice has all melted, the stone sinks to the bottom of the glass. What will happen to the level of the water in the glass, firstly as the ice melts, and secondly as the stone is released from the ice and sinks to the bottom? The water in the glass will
A. remain the same then rise
B. rise and fall
C. fall then remain the same
D. remain the same then fall

The answer is C but why?


Surely the answer is D
Original post by KatieAlicexxx
Ice takes up 33% more space than water due to its molecular arrangement. It would fall as the ice melts as this space will have been filled up again- at least that's the only explanation I can think of


Posted from TSR Mobile


That's true, but that's only the case when the temperature of the ice goes below -5 degrees I think.
Reply 5
Avatar for nickmurp
nickmurp
7
Water expands when it freezes and shrinks when it melts. The ice cube melts so the level of water falls, but the stone has never changed volume, before or after the ice melts so it always displaces the same amount of water.
(edited 8 years ago)
Original post by nickmurp
Water expands when it freezes and shrinks when it melts. The ice cube melts so the level of water falls, but the stone has never changed volume, before or after the ice melts so it always displaces the same amount of water.


But that's assuming that the whole of ice is in the water though. If the part of ice not immersed in the water had more volume when melted than the difference between the volume of ice immersed in the water and its volume when melted then the trend would be a decrease in the level of the water and then increase
(edited 8 years ago)
Reply 7
Avatar for nickmurp
nickmurp
7
Original post by Mehrdad jafari
But that's assuming that the whole of ice is in the water though. If the part of ice not immersed in the water had more volume when melted than the difference between the volume of ice immersed in the water and its volume when melted then the trend would be a decrease in the level of the water and then increase


You can assume the ice cube is fully submersed. I know it would actually float. But unless this is degree level, you'd need some complex maths to work out displacement etc..

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