Math gurus, I need your help.

[DLI848]

An object has a mass of 10.5 g. When it is submerged in a graduated cylinder initially containing 82.5 mL of water, the water level rises to 95.0 mL. What is the density of the object?

All I know is the density formula: d=m/v

[hbarcat]

First you have to count the molecules in the dissolved substance.
Then divide by the number of electrons in the outer shell.

Wait, never mind. I got this confused with a joke about a dairy farmer.

[fdeck]

In that formula, what do you know, and what don't you know?

What does the rise in water level tell you about the object, that you didn't know before?

[flipper_gv]

95-82.5=12.5 ml (volume of object)

10.5g/1000 = 0.0105 kg

1 ml = 1cm^3 (cm squared)

12.5ml/(100cm/m*100cm/m*100cm/m) = 0.0000125 m^3 (meters squared)

0.0105 kg/0.0000125m^3 = 840 kg/m^3

[MikeyFingers]

^Don't you mean cm cubed?

[bassybill]

Doesn't your teacher cover how to do this in class?

By just posting the question here without explaining why you're having difficulty, or what you've done so far and why you're stuck, you're not asking for help so much as asking to have your homework done for you. In the medium and long term this is going to be no help to you at all.

If you want to learn how to do what is, in all honesty, pretty basic stuff like this, and not be functionally crippled by a very low level of numeracy in your adult life, then try listening to your teacher in class and then thinking how to tackle stuff when you sit down to your homework instead of just posting it straight up on to TB without even a word about what's causing you the difficulty.

I suggest you don't use the solution already posted here as it will be really obvious to your teacher that you haven't done this yourself.

By the way, anybody spot anything interesting about these figures from a physics point of view? (Hint - the density of the object is lower than that of water. Not a dealbreaker, but something to think about when you consider the method used to determine the volume.)

[flipper_gv]

Originally Posted by MikeyFingers

^Don't you mean cm cubed?

both are used.

[tastybasslines]

+1
Give a man a fish and you feed him for a meal, teach him how to fish and you feed him for life.

Originally Posted by bassybill

Doesn't your teacher cover how to do this in class?

By just posting the question here without explaining why you're having difficulty, or what you've done so far and why you're stuck, you're not asking for help so much as asking to have your homework done for you. In the medium and long term this is going to be no help to you at all.

If you want to learn how to do what is, in all honesty, pretty basic stuff like this, and not be functionally crippled by a very low level of numeracy in your adult life, then try listening to your teacher in class and then thinking how to tackle stuff when you sit down to your homework instead of just posting it straight up on to TB without even a word about what's causing you the difficulty.

I suggest you don't use the solution already posted here as it will be really obvious to your teacher that you haven't done this yourself.

By the way, anybody spot anything interesting about these figures from a physics point of view? (Hint - the density of the object is lower than that of water. Not a dealbreaker, but something to think about when you consider the method used to determine the volume.)

[Cabazon]

Originally Posted by flipper_gv

both are used.

I believe he was referring to you saying,
"1 ml = 1cm^3 (cm squared)"

[bottomzone]

Originally Posted by bassybill

Doesn't your teacher cover how to do this in class?

By just posting the question here without explaining why you're having difficulty, or what you've done so far and why you're stuck, you're not asking for help so much as asking to have your homework done for you. In the medium and long term this is going to be no help to you at all.

If you want to learn how to do what is, in all honesty, pretty basic stuff like this, and not be functionally crippled by a very low level of numeracy in your adult life, then try listening to your teacher in class and then thinking how to tackle stuff when you sit down to your homework instead of just posting it straight up on to TB without even a word about what's causing you the difficulty.

I suggest you don't use the solution already posted here as it will be really obvious to your teacher that you haven't done this yourself.

By the way, anybody spot anything interesting about these figures from a physics point of view? (Hint - the density of the object is lower than that of water. Not a dealbreaker, but something to think about when you consider the method used to determine the volume.)

+100. If you don't understand the concept, you will not be able to solve other problems given to you.

A Groove is a Terrible Thing to Waste!

[MEKer]

Not that hard to figure whats going on here with the problem. But I'll say nothing further.
Look it up, talk to the teacher on what's missing. LEARN.
Relative densities, displacements, etc., etc.---not that hard.

[bassybill]

Originally Posted by Cabazon

I believe he was referring to you saying,
"1 ml = 1cm^3 (cm squared)"

I think he must have been, too.

cm squared is a unit of area and cm cubed is a unit of volume - the latter and only the latter is correct in this case.

[MEKer]

Originally Posted by bassybill

I think he must have been, too.

cm squared is a unit of area and cm cubed is a unit of volume - the latter and only the latter is correct in this case.

roger

[bassybill]

Originally Posted by bassybill

By the way, anybody spot anything interesting about these figures from a physics point of view? (Hint - the density of the object is lower than that of water. Not a dealbreaker, but something to think about when you consider the method used to determine the volume.)

Any comments?

[Orph]

Originally Posted by DLI848

An object has a mass of 10.5 g. When it is submerged in a graduated cylinder initially containing 82.5 mL of water, the water level rises to 95.0 mL. What is the density of the object?

All I know is the density formula: d=m/v

You would do well to remember Archimedes' law of buoyancy: The mass of the submerged body equals the mass of the volume of water displaced.

M=DV (density X volume, which is what you wrote).

Assuming standard conditions:

Dw (density of water at 25 deg C)~ 1000kg/m^3

Vd (volume displaced) = 12,5 x 10 ^-3 dm^3 = 12,5 x 10 ^-6 m^3

D= M/V = (0,00105g)/1,25 x 10 ^-5 m^3


Edit: ... oh, someone beat me to it.

[Orph]

Originally Posted by bassybill

Any comments?

That just means that the body isn't fully submerged, and that the density is lower than calculated. The mass of the body is correct, but without knowing the volume of the body, calculating density is meaningless.

[jp58]

Originally Posted by bassybill

Any comments?

Well it would either float, making the data for volume probably wrong, or he is only calculating the volume of the item that was submerged.

Right?

[Cabazon]

Originally Posted by bassybill

Any comments?

Perhaps the graduated cylinder is upside down.

[Chebass88]

Originally Posted by bassybill

Any comments?

Yes - I'd bet that it is a poorly constructed problem rather than an attempt to trick the student. A better second volume would have been 92.5mL, which would give something that would sink in water, i.e., rho = 1.05

Alternatively, an appropriate problem statement would have included ethanol as the test fluid, as the maths would yield a density that would remain submerged.

Chebass88

P.S. In light of all the math problems being posted, I desperately wanted to post some tensor math I'm struggling with, but that might be too much. Besides, I have to learn to fish.

[byoung]

Originally Posted by tastybasslines

+1
Give a man a fish and you feed him for a meal, teach him how to fish and you feed him for life.

Give a man a fire, and you warm him for a time; light a man on fire, and he'll be warm for the rest of his life.