The deformation of a body on application of a force depends on the nature of the material and the magnitude of the applied force.
42.
A glass capillary tube is of the shape of a truncated cone with an apex angle $$\alpha $$ so that its two ends have cross sections of different radii. When dipped in water vertically, water rises in it to a height $$h,$$ where the radius of its cross section is $$b.$$ If the surface tension of water is $$S,$$ its density is $$\rho ,$$ and its contact angle with glass is $$\theta ,$$ the value of $$h$$ will be ($$g$$ is the acceleration due to gravity)-
A
$$\frac{{2S}}{{b\rho g}}\cos \left( {\theta - \alpha } \right)$$
B
$$\frac{{2S}}{{b\rho g}}\cos \left( {\theta + \alpha } \right)$$
C
$$\frac{{2S}}{{b\rho g}}\cos \left( {\theta - \frac{\alpha }{2}} \right)$$
D
$$\frac{{2S}}{{b\rho g}}\cos \left( {\theta + \frac{\alpha }{2}} \right)$$
43.
A wooden block, with a coin placed on its top, floats in water as shown in figure. The distance $$\ell $$ and $$h$$ are shown here. After some time the coin falls into the water. Then-
$$\ell $$ decreases as the block moves up $$h$$ will also decreases because when the coin is in water it will displace a volume of water, equal to its own volume, whereas when it is on the block it displaces more volume than to own volume (because density of coin is greater than density of water).
44.
The pressure at the bottom of a tank containing a liquid does not depend on
$$P = h\rho g$$ i.e. pressure does not depend upon the area of bottom surface.
45.
The force acting on a window of area $$50\,cm \times 50\,cm$$ of a submarine at a depth of $$2000\,m$$ in an ocean, interior of which is maintained at sea level atmospheric pressure is
(Density of sea water $$ = {10^3}kg{m^{ - 3}},g = 10\,m{s^{ - 2}}$$ )
The pressure outside the submarine is
$$P = {P_a} + \rho gh$$
Pressure inside the submarine is $${P_a}.$$
Net pressure acting on the window is
$$\eqalign{
& {P_g} = P - {P_a} = \rho gh \cr
& = {10^{ - 3}}kg{m^{ - 3}} \times 10\,m{s^{ - 2}} \times 2000\,m \cr
& = 2 \times {10^7}Pa \cr} $$
Area of window is
$$A = 50\,cm \times 50\,cm = 2500 \times {10^{ - 4}}{m^2}$$
Force on the window is
$$\eqalign{
& F = {P_g}A = 2 \times {10^7}Pa \times 2500 \times {10^{ - 4}}{m^2} \cr
& = 5 \times {10^6}N \cr} $$
46.
Two parallel and opposite forces, each of magnitude $$4000\,N$$ are applied tangentially to the upper and lower faces of a cubical metal block $$25\,cm$$ on aside. The angle of Shear is [shear modulas of metal is $$80\,G\,Pa$$ ]
47.
A uniform wooden stick of length $$L,$$ cross-section area $$A$$ and density $$d$$ is immersed in a liquid of density $$4d.$$ A small body of mass $$m$$ and negligible volume is attached at the lower end of the rod so that the stick floats vertically in stable equilibrium then
48.
A hemispherical portion of radius $$R$$ is removed from the bottom of a cylinder of radius $$R.$$ The volume of the remaining cylinder is $$V$$ and its mass $$M.$$ It is suspended by a string in a liquid of density $$\rho $$ where it stays vertical. The upper surface of the cylinder is at a depth $$h$$ below the liquid surface. The force on the bottom of the cylinder by the liquid is-
For a beam, the depression at the centre is given by, $$\delta = \left( {\frac{{fL}}{{4Yb{d^3}}}} \right)\,\,\left[ {f,L,b,d\,{\text{are constants for a particular beam}}} \right]$$
$${\text{i}}{\text{.e}}{\text{.}}\,\delta \propto \frac{1}{Y}$$
50.
An iceberg is floating in ocean. What fraction of its volume is above the water ? (Given : density of ice $$ = 900\,kg/{m^3}$$ and density of ocean water $$ = 1030\,kg/{m^3}$$ )
Let $$V$$ be the volume of iceberg and let $$x$$ be the fraction of volume above water.
Using law of floatation, weight of floating body = weight of liquid displaced by part of the floating body inside the liquid.
Therefore, $$V{\rho _{{\text{ice}}}}g = \left( {1 - x} \right)V{\rho _{{\text{water}}}}g.$$
Using the value of $${\rho _{{\text{ice}}}}$$ and $${\rho _{{\text{water'}}}}$$ We get $$x = \left( {\frac{{13}}{{103}}} \right)$$