Quick Review Flashcards - Click to flip and test your knowledge!
Question
What is the name of the upward force exerted on a body by the fluid in which it is submerged?
Answer
Upthrust (or buoyant force).
Question
What is the standard symbol used to denote upthrust?
Answer
$F_B$
Question
The property of a liquid to exert an upward force on a body immersed in it is known as _____.
Answer
Buoyancy
Question
How does the magnitude of the force required to push a can into water change as more of the can is submerged?
Answer
The required force increases as the submerged volume increases.
Question
When a body is completely immersed in a fluid, the upthrust reaches its _____ value.
Answer
Maximum
Question
What happens to a piece of cork pushed into water and then released?
Answer
It rises to the surface and floats.
Question
Define 'Apparent weight' of an object in a fluid.
Answer
The weight an object seems to have when placed in a fluid, which is its real weight minus the upthrust.
Question
What is the mathematical formula for Apparent weight?
Answer
$Apparent\ weight = Real\ weight - Upthrust$
Question
Why does a bucket of water feel lighter when it is inside a well compared to when it is in the air?
Answer
The bucket experiences an upward force (upthrust) due to the water.
Question
What are the two vertical forces acting on a body submerged in a liquid?
Answer
Its weight ($W$) acting downwards and the upthrust ($F_B$) acting upwards.
Question
Under what condition regarding forces $W$ and $F'_B$ will a body sink?
Answer
A body sinks if its weight ($W$) is greater than the maximum upthrust ($F'_B$).
Question
If the maximum upthrust ($F'_B$) is greater than the weight ($W$) of a body, how will the body behave when released?
Answer
It will float with only a portion of its volume submerged.
Question
What is the net force acting on a floating body?
Answer
Zero
Question
What is the S.I. unit of upthrust?
Answer
Newton ($N$)
Question
How does the volume of the submerged part of a body affect the upthrust it experiences?
Answer
The larger the submerged volume, the greater the upthrust.
Question
How does fluid density affect the upthrust on a submerged body of the same volume?
Answer
The denser the fluid, the greater the upthrust.
Question
Where does the upthrust act on a body in relation to the displaced fluid?
Answer
Upward at the centre of buoyancy (the centre of gravity of the displaced fluid).
Question
Why does a pebble fall faster through air than a bunch of feathers of the same mass?
Answer
The feathers experience greater upthrust because they have a larger volume.
Question
In a vacuum, how do a bunch of feathers and a pebble fall relative to each other?
Answer
They fall together because there is no upthrust in a vacuum.
Question
Why does a denser liquid exert a greater upthrust for the same submerged volume?
Answer
Upthrust is proportional to the density of the fluid.
Question
What is the primary cause of upthrust in a liquid?
Answer
The difference in liquid pressure between the upper and lower surfaces of the submerged body.
Question
Formula for pressure ($P$) at depth $h$ in a liquid of density $\rho$ is _____.
Answer
$P = h \rho g$
Question
Mathematically, upthrust ($F_B$) is equal to the product of volume ($V$), fluid density ($\rho$), and _____.
Answer
Acceleration due to gravity ($g$)
Question
State Archimedes' principle.
Answer
When a body is immersed partially or completely in a liquid, it experiences an upthrust equal to the weight of the liquid displaced by it.
Question
Does Archimedes' principle apply to gases as well as liquids?
Answer
Yes, it applies to all fluids (liquids and gases).
Question
In the experimental verification of Archimedes' principle, the loss in weight of a solid is equal to the weight of the _____.
Answer
Displaced liquid
Question
A body of density $\rho$ sinks in a liquid of density $\rho_L$ if _____.
Answer
$\rho > \rho_L$
Question
A body floats just inside the surface of a liquid when its density $\rho$ is _____ the density of the liquid $\rho_L$.
Answer
Equal to
Question
Define 'Density' of a substance.
Answer
Mass per unit volume of the substance.
Question
What is the S.I. unit of density?
Answer
$kg\ m^{-3}$
Question
What is the C.G.S. unit of density?
Answer
$g\ cm^{-3}$
Question
Convert $1\ g\ cm^{-3}$ to the S.I. unit of density.
Answer
$1000\ kg\ m^{-3}$
Question
How does an increase in temperature typically affect the density of a substance?
Answer
Density usually decreases as temperature increases (due to expansion).
Question
At what temperature is the density of water at its maximum?
Answer
$4^\circ C$
Question
Define 'Relative Density' (R.D.).
Answer
The ratio of the density of a substance to the density of water at $4^\circ C$.
Question
What is the unit for Relative Density?
Answer
It has no unit (it is a pure ratio).
Question
In the C.G.S. system, how does the numerical value of Relative Density relate to density?
Answer
Relative Density is equal to the numerical value of density in $g\ cm^{-3}$.
Question
Using weights, what is the formula for the Relative Density of a solid denser than water?
Answer
$R.D. = \frac{Weight\ of\ body\ in\ air}{Loss\ in\ weight\ of\ body\ in\ water}$
Question
If $W_1$ is weight in air and $W_2$ is weight in water, what is the formula for R.D.?
Answer
$R.D. = \frac{W_1}{W_1 - W_2}$
Question
How can you find the R.D. of a solid that is soluble in water?
Answer
Use a liquid in which the solid is insoluble and multiply the calculated ratio by the R.D. of that liquid.
Question
State the Principle of Floatation.
Answer
The weight of a floating body is equal to the weight of the liquid displaced by its submerged part.
Question
For a floating body, what is the value of the apparent weight?
Answer
Zero
Question
What is the relationship between the submerged volume ($v$), total volume ($V$), body density ($\rho_s$), and liquid density ($\rho_L$) for a floating body?
Answer
$\frac{v}{V} = \frac{\rho_s}{\rho_L}$
Question
Why does an iron ship float while an iron nail sinks in water?
Answer
The ship is hollow and contains air, making its average density less than that of water.
Question
A loaded ship is submerged _____ than an unloaded ship.
Answer
More
Question
What is the purpose of the 'Plimsoll line' on a ship?
Answer
It indicates the safe limit for loading the ship in water of different densities.
Question
Why does a ship sink further when it sails from sea water into river water?
Answer
River water is less dense than sea water, so a larger volume must be displaced to balance the ship's weight.
Question
What is used as 'ballast' in an unloaded ship to lower its centre of gravity?
Answer
Sand or stones filled at the bottom.
Question
Why is it easier to swim in sea water than in fresh water?
Answer
Sea water is denser due to dissolved salts, providing a greater upthrust.
Question
How does a submarine dive underwater?
Answer
Its ballast tanks are filled with water to increase its average density beyond that of sea water.
Question
Roughly what percentage of an iceberg remains submerged in sea water?
Answer
Approximately $89.3\%$ (or about $90\%$).
Question
Why are icebergs dangerous for ships?
Answer
Most of the iceberg is submerged (hidden), making it difficult to estimate its size and avoid collision.
Question
What organ in a fish acts like the ballast tank of a submarine?
Answer
The swim bladder.
Question
A balloon filled with hydrogen rises because the upthrust is _____ than the weight of the balloon.
Answer
Greater
Question
Why does a rising balloon eventually stop rising?
Answer
The density of air decreases with altitude, so upthrust decreases until it equals the balloon's weight.
Question
What is the formula for the Relative Density of a liquid using a solid displacement method?
Answer
$R.D.\ of\ liquid = \frac{W_1 - W_3}{W_1 - W_2}$ (where $W_1$ is weight in air, $W_2$ in water, and $W_3$ in the liquid).
Question
If a body floats in a liquid, how does the density of the body compare to the density of the liquid?
Answer
The density of the body is less than or equal to the density of the liquid.
Question
The centre of buoyancy coincides with the centre of gravity of the body only if the body is _____.
Answer
Completely immersed (and uniform).
Question
True or False: The upthrust on a body depends on the mass of the body.
Answer
False (it depends on the volume of the submerged part and the density of the fluid).
Question
What happens to the level of water when a floating piece of ice melts?
Answer
The water level remains unchanged.