Floating and Sinking

Q.

The time required for light to pass through a glass slab of $2mm$ thickness is (${\mu }_{glass}=1.5$)

1. ${10}^{-8} s$

2. ${10}^{-6} s$

3. ${10}^{-11} s$

4. none of these

Q. Floating and sinking depend on ___ of water and object.

Q.

A piece of wood if left under water, comes to the surface. Explain the reason.

Q. What happens to the buoyant force acting on an airship as it rises in the air?

1. Buoyant force increases
2. Buoyant force decreases
3. Buoyant force remains constant
4. Buoyant force first increases then shows decrease

Q.

Why does an object lose its weight when immersed in a liquid?

Q. A block of iron sinks in fluid A but floats in fluid B, this is because fluid A is than fluid B.

1. more denser
2. less denser
3. more viscous

Q.

The centre of gravity and the centre of buoyancy of a floating body in stable equilibrium

(i) are always same

(ii) are always along a same vertical line

1. only (i) is true

2. only (ii) is true

3. Both (i) and (ii) are correct

4. only (i) is false

Q. A cube of side 10 cm completely immersed in water experiences a buoyant force of 1000 N. Take $g=10m/s^2$.

1. True
2. False

Q.

6. List all items known to you that float on water. Check and see if they will float on an oil or kerosene.

Q.

A body weighs 200 gf in air and 175 gf when it is completely immersed in water. The buoyancy force acting on it is

1. 25 g

2. 2.5 g

3. 25 kg

4. 2.5 kg

Q. Objects having relative density greater than 1 _____ in water.

1. sink
2. float
3. oscillates up and down
4. may sink or float

Q. The specific gravity of a material is 0.76, it will:

1. None of the above
2. Sink in water
3. Float in water
4. Accelerate in water

Q.

A solid weighs $100N$ in the air and $90N$ when completely immersed in water. Calculate the volume of the solid.

Take acceleration due to gravity $g$ = $10m/s^2$

1. 
2. 
3. 
4. 

Q.

A block of wood is so loaded that it just floats in water at room temperature. What change will occur in the state of floatation, if (a) some salt is added to water, (b) water is heated ? Give reason.

Q.

A block of wood is floating in the water. The portion of the block inside water measures 50 cm x 50 cm x 50 cm. What is the magnitude of the buoyant force acting on the block? (Take the density of water as 1 g cm-3)

Q.

Wood charcoal can float on water.

1. True
2. False

Q. A body of volume 100 c$m^3$ weighs 5 kg in air. It is completely immersed in a liquid of density 1.8 x ${10}^3$ kg/$m^3$. Find the apparent weight of the body in the liquid.

1. 4.82 kgf
2. 5 kgf
3. 18 kgf
4. 5.82 kgf

Q.

Archimedes principle describes the magnitude of buoyant force acting on a body that is partially or completely submerged in a liquid.

1. True
2. False

Q.

A body of density $\rho$ sinks in a liquid of density ${\rho }_L$. The densities $\rho$ and ${\rho }_L$ , are related as :
(a) $\rho$ = ${\rho }_L$ (b) $\rho$ < ${\rho }_L$
(c) $\rho$ > ${\rho }_L$ (d) nothing can be said.

Q. A solid cube of side $a=5cm$ has a mass of $M=1000g$. It is recasted into a hollow cube of side $b$ with air inside. What should be the minimum value of $b$, so that this hollow cube floats in this water?
Consider air mass in cylinder to be negligible.

1. $b=5cm$
2. $b=20cm$
3. $b=8cm$
4. $b=10cm$

Q. Liquid A and liquid B exerts the same amount of pressure and density of liquid A is twice the density of liquid B. What would be the height of the column of liquid A if the height of the column of liquid B is 10cm?

1. 5 cm
2. 15 cm
3. 10 cm
4. 20 cm

Q.

Two hard metal spheres of the same material, of the density $\mathrm{\rho }$, and of equal radius R are just touching each other. Calculate the force of gravitational attraction between them.

Q.

A cube of side 5 cm is immersed in water and then in a saturated salt solution. In which case will it experience a greater buoyant force. If each side of the cube is reduced to 4 cm and then immersed in water, what will be the effect on the buoyant force experienced by the cube as compared to the first case for water. Give the reason for each case.

Q.

Find the density of a substance if its volume is $300c{m}^3$and mass $60g.$

Q. The density of gold is $19.3\times {10}^3{\text{kg/m}}^3$.
A plate made of gold was kept in a museum stating that it is of pure gold. The weight of this plate was $83.2\text{N}$. To test its purity it was immersed in water. If it was genuine real gold then how much it should weigh in water?

Q. In which direction does the buoyant force act (if the weight is acting downwards)?

1. Upwards

2. Downwards

3. Perpendicular to the direction of the weight

4. At an acute angle to the downward direction

Q.

Density of a material is equal to its mass divided by its volume. What is the density (in $kg{m}^{-3}$) of a rock of mass $1.8kg$ and volume $6\times {10}^{-4}{m}^3$?

Q. Body A of density $\left({\rho }_A\right)$ is floating in the water. When another body B having density $({\rho }_B=1500kg{m}^{-3})$ and same dimensions is placed on body A, then the system just sinks in the water. What fraction of body A was originally immersed in the water?
The density of water is ${\rho }_w=1000kg{m}^{-3}$.

1. 0.5

Q. The body when immersed fully or partially in a fluid, experiences an upward force, equal to ............. of displaced fluid.

1. Mass
2. Weight
3. Volume
4. Area

Q.

A homogeneous block floats on water (a) partly immersed (b) completely immersed. In each case state the position of the centre of buoyancy B with respect to the centre of gravity G of the block.