LukasMcNeal Posted September 27, 2012 Report Share Posted September 27, 2012 I think im being retarded or just lost the plot. The question is : Calculate the apparent weight of 12kg of iron immersed in water. I am given density of iron : 7800kgm^-3 and density of water 1000kgm^-3 Surely I need to know the volume of the piece of iron? Ive been staring at my physics notes for ages and ive gone mindblank. I know it involves archimedes but I swear I need the volume? Quote Link to comment Share on other sites More sharing options...
dann2707 Posted September 27, 2012 Report Share Posted September 27, 2012 (edited) You can work out the volume of the Iron as you know how much it weighs and you know it's density. Edit - maybe. Edited September 27, 2012 by dann2707 Quote Link to comment Share on other sites More sharing options...
AndrewEH1 Posted September 27, 2012 Report Share Posted September 27, 2012 (edited) Can you not work out the volume, if you need it, as you have both the weight and the density. Divide one into the other? Density = mass/volume? Edit: I have no actual idea how to solve this, stop doing physics 5/6 years ago... Edited September 27, 2012 by AndrewEH1 Quote Link to comment Share on other sites More sharing options...
LukasMcNeal Posted September 27, 2012 Author Report Share Posted September 27, 2012 I thought to get the volume you needed to know like the length etc. Quote Link to comment Share on other sites More sharing options...
trialsiain Posted September 27, 2012 Report Share Posted September 27, 2012 v=st Quote Link to comment Share on other sites More sharing options...
LukasMcNeal Posted September 27, 2012 Author Report Share Posted September 27, 2012 And s and t equal? Quote Link to comment Share on other sites More sharing options...
monkeyseemonkeydo Posted September 27, 2012 Report Share Posted September 27, 2012 Yeah, I think you need to work out the volume from mass and density then the buoyancy is equal to the weight of water displaced (I think, been a looooooong time since I did this stuff!). You've then got gravity pulling the iron down and buoyancy pushing it up giving the apparent weight of the iron. That's what I'd be doing, anyway. Edit: for shapes and stuff you would usually do length x breadth x height or whatever but if given any two of mass, volume and density you can work out the third since they are simply related. 1 Quote Link to comment Share on other sites More sharing options...
casualjoe Posted September 27, 2012 Report Share Posted September 27, 2012 Could be worth a watch.. Quote Link to comment Share on other sites More sharing options...
trialsiain Posted September 27, 2012 Report Share Posted September 27, 2012 And s and t equal? ahah i was joking i learned that in 3rd year or somehting... s & t = speed and time.. but now we use scalor or summit Quote Link to comment Share on other sites More sharing options...
LukasMcNeal Posted September 27, 2012 Author Report Share Posted September 27, 2012 Thanks for that Quote Link to comment Share on other sites More sharing options...
RobinJI Posted September 27, 2012 Report Share Posted September 27, 2012 (edited) v=st Are you thinking of v=s/t? In which instance v = velocity, s = distance and t = time? As for the original question, basically what monkeyseemonkeydo said. It's boyancy is equivilent to the weight of water it's displaced, and it's volume is its mass divided by its density. So that makes it's volume 12/7800 = 0.001538m^3, which makes it's boyancy 0.001538*1000 = 1.5385kg, giving a final apparent imersed weight of 12 - 1.5385 = 10.4615kg. Edited September 27, 2012 by RobinJI Quote Link to comment Share on other sites More sharing options...
LukasMcNeal Posted September 27, 2012 Author Report Share Posted September 27, 2012 Thanks alot! I get that now! Quote Link to comment Share on other sites More sharing options...
Matt Vandart Posted September 27, 2012 Report Share Posted September 27, 2012 Trials forum helping kids cheat since 2012...... 1 Quote Link to comment Share on other sites More sharing options...
LukasMcNeal Posted September 27, 2012 Author Report Share Posted September 27, 2012 (edited) Hahah im not cheating! Im missing part of my notes and my last lesson was a week a go so couldnt remember for my homework! Edited September 27, 2012 by LukasMcNeal Quote Link to comment Share on other sites More sharing options...
monkeyseemonkeydo Posted September 28, 2012 Report Share Posted September 28, 2012 final apparent imersed weight of 12 - 1.5385 = 10.4615kg. Are you sure about that?... Quote Link to comment Share on other sites More sharing options...
Matt Vandart Posted September 28, 2012 Report Share Posted September 28, 2012 I'm all for cheating fella! Quote Link to comment Share on other sites More sharing options...
Revolver Posted September 28, 2012 Report Share Posted September 28, 2012 You naughty man. Quote Link to comment Share on other sites More sharing options...
LukasMcNeal Posted September 28, 2012 Author Report Share Posted September 28, 2012 I done it properly: Iron: ρ 7800kgm^-3 m 12kgm^-3 v 12/7800 = 1/650m^3 iron weight 12 x 9.81 = 117.72 upthrust ρf x v x g = 7800 x 1/650 x 9.81 = 15.09n weight is 117.72n and upthrust is 15.09n thus apparent weight is 117.72-15.09= 102.63n 2 Quote Link to comment Share on other sites More sharing options...
RobinJI Posted September 28, 2012 Report Share Posted September 28, 2012 Are you sure about that?... haha, hadn't spotted that, it's because I didn't round during the calculations, I just rounded each number as I wrote it down, so it's written to 4 sygnificant figures, but calculated using the true values, the answer's right anyway! Your answer looks good anyway Lucas Quote Link to comment Share on other sites More sharing options...
monkeyseemonkeydo Posted September 29, 2012 Report Share Posted September 29, 2012 haha, hadn't spotted that, it's because I didn't round during the calculations, I just rounded each number as I wrote it down, so it's written to 4 sygnificant figures, but calculated using the true values, the answer's right anyway! Sorry, I was meaning that the weight wouldn't be in kg's . 1 Quote Link to comment Share on other sites More sharing options...
casualjoe Posted September 29, 2012 Report Share Posted September 29, 2012 Gotta love physics. Did you know that a major component of the force of friction is a newly discovered drag caused by the alignment of the 'spin' of atomic nuclei in the atoms making up the two surfaces. Along with electrical and heat forces of course. Quote Link to comment Share on other sites More sharing options...
RobinJI Posted September 29, 2012 Report Share Posted September 29, 2012 Ahh, true. Well I know what I meant Quote Link to comment Share on other sites More sharing options...
Tony Harrison Posted September 29, 2012 Report Share Posted September 29, 2012 I done it properly: You DID it properly. As in, I DID IT, I DIDN'T DO IT. The most simplest f**king word in the dictionary, and yet every kid f'cks it up ALL THE TIME. Quote Link to comment Share on other sites More sharing options...
LukasMcNeal Posted September 29, 2012 Author Report Share Posted September 29, 2012 Hey I don't take AS English Quote Link to comment Share on other sites More sharing options...
Revolver Posted September 29, 2012 Report Share Posted September 29, 2012 On the other hand you're still old enough to know better, and it is your mother tongue. Quote Link to comment Share on other sites More sharing options...
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