The apparent weight
I am puzzled by this question
What is the apparent weight for a piece of wood has density 1.10 g/cm3 if it displaced 786 ml from water when it was immersed in lake
What is the apparent weight for a piece of wood has density 1.10 g/cm3 if it displaced 786 ml from water when it was immersed in lake
Original post by MAA_96
I am puzzled by this question
What is the apparent weight for a piece of wood has density 1.10 g/cm3 if it displaced 786 ml from water when it was immersed in lake
What is the apparent weight for a piece of wood has density 1.10 g/cm3 if it displaced 786 ml from water when it was immersed in lake
Archimedes Principle states that the wood will experience an upwards force (upthrust) due to the weight of the water it displaces.
Find the weight of 786ml water. This is the reduction in the measured weight of the wood.
The wood's normal weight can be found from its mass. (Volume x density)
The clue is in the 'displaced 786 ml of water' statement and the difference in density between the wood and water.
You know that the wood will float on water when the force of gravity pulling it down (it's weight) is equal to the 'upthrust' of the water stopping it from being pulled down any further. (Archimedes). At that point the forces on the wood are balanced.
When that happens the amount of water displaced will be exactly the same as the weight of the wood.
So to answer the question you need to know:
a) How to convert 786 ml of water into cm3 of water.
b) What the weight of 786 ml of water is.
c) Using this information, work out the 'apparent' weight of the wood.
You know that the wood will float on water when the force of gravity pulling it down (it's weight) is equal to the 'upthrust' of the water stopping it from being pulled down any further. (Archimedes). At that point the forces on the wood are balanced.
When that happens the amount of water displaced will be exactly the same as the weight of the wood.
So to answer the question you need to know:
a) How to convert 786 ml of water into cm3 of water.
b) What the weight of 786 ml of water is.
c) Using this information, work out the 'apparent' weight of the wood.
Original post by uberteknik
The clue is in the 'displaced 786 ml of water' statement and the difference in density between the wood and water.
You know that the wood will float on water when the force of gravity pulling it down (it's weight) is equal to the 'upthrust' of the water stopping it from being pulled down any further. (Archimedes). At that point the forces on the wood are balanced.
When that happens the amount of water displaced will be exactly the same as the weight of the wood.
So to answer the question you need to know:
a) How to convert 786 ml of water into cm3 of water.
b) What the weight of 786 ml of water is.
c) Using this information, work out the 'apparent' weight of the wood.
You know that the wood will float on water when the force of gravity pulling it down (it's weight) is equal to the 'upthrust' of the water stopping it from being pulled down any further. (Archimedes). At that point the forces on the wood are balanced.
When that happens the amount of water displaced will be exactly the same as the weight of the wood.
So to answer the question you need to know:
a) How to convert 786 ml of water into cm3 of water.
b) What the weight of 786 ml of water is.
c) Using this information, work out the 'apparent' weight of the wood.
But what do you mean in step "a"? They are basically the same ml and cm^3.
Original post by MAA_96
But what do you mean in step "a"? They are basically the same ml and cm^3.
Yes.
The statement was to check your understanding that ml's apply to liquids which therefore take up the shape of their container, whereas cm3 is a volume with dimensions 1 x 1 x 1 cm. So as you point out, 1cm3 is a defined shape = 1 ml in any shape.
(edited 11 years ago)
Original post by uberteknik
Yes. The statement was to check your understanding that ml's apply to liquids which therefore take up the shape of their container, whereas cm3 is a volume with dimensions 1 x 1 x 1 cm.
So as you point out, 1cm3 is a defined shape = 1 ml in any shape.
The statement was to check your understanding that ml's apply to liquids which therefore take up the shape of their container, whereas cm3 is a volume with dimensions 1 x 1 x 1 cm. So as you point out, 1cm3 is a defined shape = 1 ml in any shape.
that's what I thought but I have one more question .How can I find the weight of the water in step "b" do I have to only multiply by 9.8 ?
(edited 11 years ago)
Original post by MAA_96
that's what I thought but I have one more question .How can I find the weight of the water in step "b" do I have to only multiply by 9.8 ?
Mass = Volume x Density
Force = Mass x Acceleration
Weight = Mass x Acceleration due to gravity
So yes to work out the weights, you need to use acceleration due to gravity = 9.81 m/s2
Apparent weight is given by the formula:
actual weight of object - weight of displaced liquid
You already have the volume of water displaced in ml so convert that to cm3 to get the volume of the wood in cm3.
You can work out the actual weight of the wood by using:
weight = density x volume x gravity. (plug in the numbers for the density and volume of the wood and the)
You can also work out the weight of the water displaced by the same formula but you need to know the density of water to do that.
Once you have both of those weights, you cab plug them both into the apparent weight formula and you have your answer.
(edited 11 years ago)
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