Tag: applications of floatation

Questions Related to applications of floatation

A person of mass $m$ is standing on one end of a plank of mass $M$ and length $L$ and floating in water. The person moves from one end to another and stops. The displacement of the plank is :

  1. $\dfrac {Lm}{(m+M)}$

  2. $Lm(M+m)$

  3. $\dfrac {(m+M)}{Lm}$

  4. $\dfrac {LM}{(m+M)}$


Correct Option: A

A cube of 3 side L floats in a liquid of density 3 times the density of cube. What length of the cube will out side the liquid?

  1. $\dfrac{L}{3}$

  2. $\dfrac{2L}{3}$

  3. $\dfrac{2L}{5}$

  4. $\dfrac{L}{5}$


Correct Option: C

A wire of length L M made a material of specific gravity 8 is floating horizontally on the surface of water. If it is not wet by water the maximum diameter of the wire in millimetre which it can continue to floaters

  1. 1.5

  2. 1.1

  3. 0.75

  4. 0.55


Correct Option: C

If an ice cube a with impurities is floating in the water container and after few minutes ice melts and impurities  are sink down then find the level of water in that container :

  1. increased

  2. decreased

  3. same

  4. may increased or decreased


Correct Option: A

A beaker containing water weighs $100$ g. It is placed on the pan of a balance and a piece of metal  weighing 70 g and having a volume of $10c{m^3}$ is placed inside the water in beaker. The weight of the beaker and the metal would be:

  1. $170g$

  2. $160$g

  3. $100$g

  4. $30g$


Correct Option: B

equal to the weight of the immersed part of the body 2 . A raft of wood of mass 120 kg floats in water . The weight C that can be on the raft on make it just sink , should be $(d _{raft} = 600 kg/m _{3} )$

  1. 80 kg

  2. 50 kg

  3. 60 kg

  4. 30 kg


Correct Option: C

A wooden cube floating in water supports a mass $0.2 kg$ When the mass is removed the cube rises by $2 cm.$ The side of the cube is (density of water=${10^3}kg/{m^3}$)

  1. $6 cm$

  2. $12 cm$

  3. $8 cm$

  4. $10 cm$


Correct Option: B

The material of wire has specific gravity 8. It is not wetted by water, what is the diameter of the wire that will float on the surface of water?(T =70 dy /cm)

  1. 15 mm

  2. 1.5 cm

  3. 1.3

  4. None of these


Correct Option: B

A ball rise with constant velocity, to the surface of a liquid whose density is four times that of the ball. The ratio of the v force to weight of the ball is

  1. 1

  2. 2

  3. 3

  4. 4


Correct Option: C

A balloon has volume of 1000 $m^{3}$ . It is filled with hydrogen ($ \rho $ = 0.09 g/L ) . If the density of air is 1.29 g/L , it can lift a total weight of 

  1. 600 kg

  2. 1200 kg

  3. 300 kg

  4. 1800 kg


Correct Option: B
Explanation:
Given,
$V _b=1000m^3$
$\rho _h=0.09g/L$
$\rho _a=1.29g/L$
$g=10m/s^2$
Upthrust force = total downward force
$V _b \rho _a h=mg+\rho _h V _b g$
$1000\times 1.29\times 10=mg+0.09\times 1000\times 10$
$1290=mg+90$
$mg=1200kg-weight$
The correct option is B.