On 6 Sep 2017 at 7:59am Mark wrote:
If I had an aquarium with water in it weighing 100kg and I put a Carp that weighs 10kg in it what would the aquarium now weigh?
On 6 Sep 2017 at 8:08am Answer wrote:
It weights less than 100kg as it's just the aquarium you are asking about. So how much did the water weight then you can work it out.
On 6 Sep 2017 at 8:16am Boffin wrote:
The same. Adding a fish does not increase the 'aquarium' weight, that remains constant.
On 6 Sep 2017 at 8:25am Mark wrote:
Alright then... What is the combined weight of the fish, water and aquarium?
On 6 Sep 2017 at 9:21am Jeff wrote:
110kg + weight of aquarium
On 6 Sep 2017 at 9:23am Clifford wrote:
Is the answer Geneva?
On 6 Sep 2017 at 10:12am Ed Can Do wrote:
100kg of water with a 10kg fish in weight a combined 110kg. Being in water doesn't make you weigh any less but the total volume also increases so the water level rises by the volume of the fish.
On 6 Sep 2017 at 10:28am Tom wrote:
Depends on the level of the water. If it's at the top then the amount of water displaced will be equal to the weight of the fish. So the weight will remain the same (100kg). If the waterline is below the edge of the tank then that's a different answer
On 6 Sep 2017 at 12:21pm Deja Vu wrote:
Boffin is the only one that is correct.
Aquarium weight = unknown
Water weight = 100kg
Fish weight = 10kg
It's not possible to work out the "combined total weight" as the weight of the aquarium isn't known, but adding water and a fish does not change the weight of the aquarium, it weights what it weighs.
The question is ambiguous, it is not clear if 100kg is the weight of the water or the water and tank, you have to assume it is only the water due to the way it is phrased (and the missing comma after the first "it").
On 6 Sep 2017 at 12:28pm VSauce wrote:
That's either a very shallow or small aquarium. I would suggest a smaller fish.
On 6 Sep 2017 at 12:43pm Tom wrote:
Deja Vu, whilst you're right the question is ambiguous - lets assume it means there is 100kg of water in it + the tank weight. Let's also assume it's shape is a cube for simplicity.
100kg of water = 100 litres of water = 0.1 m^3
Therefore the length of the tank is = 0.465 m
Assuming the thickness of the glass is 5mm
From this we can then work out the volume of a sheet of glass 1.08x10^-3 m^3
Lets say the tank has 5 sides (There's no top on my tank and even if there was it'd probably be plastic) and using the density of glass as 2550 kg/m^3 (quick google search) we get the weight to be 13.5kg.
So the answer is one of:
a) The water of the tank is at the edge and the 100kg includes the weight of the aquarium: 100kg
b) The water of the tank is at the edge and the 100kg is only the weight of the water: 113.5kg
c) The water of the tank is not at the edge and the 100kg includes the weight of the aquarium: 110kg
d) The water of the tank is not at the edge and the 100kg is only the weight of the water: 123.5kg
Take your pick as to how you read the question
On 6 Sep 2017 at 2:59pm Deja Vu wrote:
@Tom, you cannot deduce the length of the tank in any way shape or form from the volume (for all you know it could be 1" long and wide, but incredibly tall), doing so would be pointless.
With regards the maths, most aquariums are high strength acrylic not glass.
You can assume nothing except what is inferred in the question, certainly you can't assume that adding a fish to a tank (even if it is FULL of water) will displace any water (have you never heard of surface tension), that largely depends on the shape of the tank or how obtuse the question is.
For example, if the tank is 1m wide, 1m long and 1cm deep the fish will be 99% out of the water and displace nothing.
But I stand by my original statement, adding water and a fish does not change the weight of the aquarium, the aquarium still weighs what it weighs.
Watch the video »
On 6 Sep 2017 at 3:27pm Manhole lifter wrote:
I lifted a manhole and there was carp floating up to the brim. Just like this forum.
On 6 Sep 2017 at 3:28pm Lid l wrote:
No, you lifted the lid on a manhole.
On 6 Sep 2017 at 3:30pm Jimmy Lidl wrote:
I had some input to that manhole, after 5 pints of Harvey's.
On 6 Sep 2017 at 4:00pm The Greek wrote:
Deja Vu and Tom are both right. The question does not provide enough information, however Tom has made sensible assumptions and stated them so his answers are valid.
However he has neglected to say that he has assumed the water to be perfectly flat at the surface, without the characteristic concave meniscus of water (water is quite "sticky" chemically) or that the surface of the tank is frictionless. He should have also mentioned that surface tension is 0 Newtons. Think "infinitely long, inextensible wire" or "frictionless surfaces" of school physics questions....
But without splitting hairs, it's a pretty good set of approximations.. (I hope my Physics degree has served me well!!)
On 6 Sep 2017 at 4:01pm The Greek wrote:
Not to mention water is rarely pure either.
On 6 Sep 2017 at 4:16pm VSauce wrote:
This of course depends on the location of the aquarium. If I was to place it at lagrange points L1 or L3 this would effectively cancel out the gravitational attraction to the earth giving it a weight of zero.
On 6 Sep 2017 at 4:38pm The Greek wrote:
^ However OP is using kilograms, so that implies they really mean mass. Its weight would vary depending on the acceleration due to gravity. So I guess the tank's weight is really 981 Newtons on Earth.
On 6 Sep 2017 at 4:45pm Mark wrote:
Thank you so much folk for the helpful answers. I was thinking that the fish would be weightless as it was floating. Like someone floating in mid air! Needless to say, I don't have a physics degree. And I'm sorry for my vague details. The combined weight of tank and water is 100kg and it is sort of shoebox lying on its side shaped. There is no displacement of water when the fish goes in.
On 6 Sep 2017 at 5:01pm The Greek wrote:
Ah so it is a real life conundrum not just a random brainteaser for the forum!
In which case, the total mass of the aquarium and fish combo would indeed by 110kg if no water leaves the tank.
The fish still experiences acceleration due to gravity (weight) although it also experiences a somewhat equal opposing force from the water causing it to float.
On 6 Sep 2017 at 5:01pm The Greek wrote:
AKA Newton's 3rd Law 
On 6 Sep 2017 at 5:05pm Sid wrote:
What weighs the most - a pound of feathers or a pound of lead?
Was it salt water by the way?
On 6 Sep 2017 at 6:38pm Local wrote:
We we know the water weighs and what the fish weighs, put the aquarium on the Scales then you can take the weight of the water of and the fish, then you will know how much the aquarium weighs.
On 6 Sep 2017 at 7:24pm Tom wrote:
@Deja Vu - Physicists wouldn't have gotten anywhere if they hadn't learnt to make assumptions. You're right though in that I should've stated I was ignoring surface tension
@The Greek - You're right I neglected to state those assumptions as well. That's what you get though from me dropping out of my Physics degree after a year and transferring to Mech Eng