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Brain Teasers 2
- Thread starter bucknast
- Start date
nech - I'll presume the refrigerator is entirely within the otherwise sealed room with nothing else.
Cooling rate is negative - fridge is heating up the room. Start with average power draw by the fridge, convert to heat. Then go forward with EngineerErrant's calcs.
Cooling rate is negative - fridge is heating up the room. Start with average power draw by the fridge, convert to heat. Then go forward with EngineerErrant's calcs.
SomptingGuy
Automotive
I was going to answer, but I thought it might be a trick question. There will be an initial transient as the two control volumes become one. That's before the steady heating effect as the thermostat in the fridges keeps the thing running. Assuming the thermostat is a two-state device, heating rate should then be constant, depending on the power rating of the fridge.
- Steve
- Steve
Sompting- Back to the displacement question, I see the smug interviewers statements as correct. If you have a bucket of water in a boat and pour it into the pond the water level is the same, the volume of boat rising above water level is the same amount as water added. If it is a brick the water level in the pond goes down as the volume of the boat rising out of the water is greater than the volume of the brick added to the pond. Or maybe I missed something?
Comprehension is not understanding. Understanding is not wisdom. And it is wisdom that gives us the ability to apply what we know, to our real world situations
Comprehension is not understanding. Understanding is not wisdom. And it is wisdom that gives us the ability to apply what we know, to our real world situations
patprimmer
New member
If the SG (which is unspecified) of the brick is greater than 1, while in the boat the weight of the brick is displaced as part of the boat.
Once the brick is removed it sinks and displaces its volume in water which is less than its weight.
If the brick is SG 1 or less it displaces its weight in water either way so no change.
Unless otherwise specified the definition of a brick is a ceramic or earthenware object used as a building material. these bricks always have an SG of more than 1.
The interviewer was less than justified in being smug, however proving that probably goes against you and reinforces "lifes not fair".
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
Once the brick is removed it sinks and displaces its volume in water which is less than its weight.
If the brick is SG 1 or less it displaces its weight in water either way so no change.
Unless otherwise specified the definition of a brick is a ceramic or earthenware object used as a building material. these bricks always have an SG of more than 1.
The interviewer was less than justified in being smug, however proving that probably goes against you and reinforces "lifes not fair".
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
GregLocock
Automotive
Unplug the fridge, open the fridge door. Room temperature drops. talking of which when are we going to get domestic fridges with remote radiators? I'm sick of sharing my house with a 400++++ W heater in summer.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376
Next you'll be suggesting to try and integrate it the AC Greg.
Posting guidelines faq731-376 (probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484
What is Engineering anyway: faq1088-1484
patprimmer
New member
Greg
I had an onsite caravan where I cut a hole in the wall the same size as the fridge. Put the fridge in with the condenser exposed to the outside then sealed the sides of the fridge to the wall of the van. Worked for me as we only used the van in summer.
I put some strategically placed trellis work to protect the condenser from passers by and vise versa.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
I had an onsite caravan where I cut a hole in the wall the same size as the fridge. Put the fridge in with the condenser exposed to the outside then sealed the sides of the fridge to the wall of the van. Worked for me as we only used the van in summer.
I put some strategically placed trellis work to protect the condenser from passers by and vise versa.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
SomptingGuy
Automotive
Displacement question. A simple thought experiment requiring no laws of physics.
1) I have a big brick of gold in the boat. The boat is close to sinking due to the huge weight of the brick and the water level in the pond is close to overflowing its banks. I throw it in. My boat is suddenly unladen, so the water level drops massively. When everything has stopped bouncing around, the level is slightly higher (volume of gold brick) than it would have been had there been no brick to start with. But lower than it was when the boat was thinking of sinking.
2) My brick is expanded polystyrene. It floats nicely on the pond. Nothing changes with the water level.
- Steve
1) I have a big brick of gold in the boat. The boat is close to sinking due to the huge weight of the brick and the water level in the pond is close to overflowing its banks. I throw it in. My boat is suddenly unladen, so the water level drops massively. When everything has stopped bouncing around, the level is slightly higher (volume of gold brick) than it would have been had there been no brick to start with. But lower than it was when the boat was thinking of sinking.
2) My brick is expanded polystyrene. It floats nicely on the pond. Nothing changes with the water level.
- Steve
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