Tag: pressure in fluids and atmospheric pressure

Questions Related to pressure in fluids and atmospheric pressure

A U-tube is partially filled with water. Oil which does not mix with water is next poured into one side, until water rises by $25\;cm$ on the other side. If the density of oil is $0.8\;g/cc$, the oil level will stand higher than the water level by

  1. $6.25\;cm$

  2. $12.50\;cm$

  3. $18.75\;cm$

  4. $25.00\;cm$


Correct Option: B

The area of the piston in hydraulic machine are $10cm^2$ and $225cm^2$. The force required on the smaller piston to support a load of $1000N$ on the larger piston.

  1. 44.44 N

  2. 55.55 N

  3. 33.33 N

  4. 4.44 N


Correct Option: A
Explanation:

$\begin{array}{l} \dfrac { f }{ { 10 } } =\dfrac { { 1000 } }{ { 225 } }  \ f=\dfrac { { 10000 } }{ { 225 } }  \ f=44.44N \end{array}$

$ \therefore$ Option $A$ is correct.

Hydraulic machines work on the application of

  1. Pascal's law

  2. Newton's law

  3. Law of Gravity

  4. none of these


Correct Option: A
Explanation:

The hydraulic machine uses Pascal's principle, which states that states that the pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid.
The hydraulic machine is used to multiple force or to transmit force from one location to another. 
i)     hydraulic brakes
ii)    hydraulic press
ii)    hydraulic lift

What should be the ratio of area of cross section of the master cylinder and wheel cylinder of a hydraulic brake so that a force of $15  N$ can be obtained at each of its brake shoe by exerting a force of $0.5  N$ on the pedal?

  1. $1: 60$

  2. $1: 30$

  3. $1: 15$

  4. $1: 45$


Correct Option: B
Explanation:

We know that $P _{1} = P _{2}$

$\Rightarrow \dfrac{F _{1}}{A _{1}} = \dfrac{F _{2}}{A _{2}} $

$\Rightarrow \dfrac{A _{1}}{A _{2}} = \dfrac{F _{1}}{F _{2}}  = \dfrac{1}{30} $

$\Rightarrow  1:30 $

In a hydraulic lift, used at a service station the radius of the large and small piston are in the ratio of $20 : 1$. What weight placed on the small piston will be sufficient to lift a car of mass $1500 kg$ ?

  1. $3.75 kg$

  2. $37.5 kg$

  3. $7.5 kg$

  4. $75 kg$


Correct Option: A
Explanation:

Answer is A.

Pressure is the amount of force acting per unit area. That is, $P=F/A$.
where:
$p$ is the pressure,
$F$ is the normal force,
$A$ is the area of the surface on contact. Let us consider A = $\pi { r }^{ 2 }$.
Therefore, $\dfrac { { F } _{ 1 } }{ { \pi { r } _{ 1 } }^{ 2 } } =\dfrac { { F } _{ 2 } }{ { \pi { r } _{ 2 } }^{ 2 } } $.
In this case, $\dfrac { 1500 }{ { 20 }^{ 2 } } =\dfrac { W }{ { 1 }^{ 2 } } ,\quad W\quad =\quad 3.75\quad kg.$
Hence, weight to be placed on the small piston sufficient to lift a car of mass 1500 kg is 3.75 kg.

To avoid vaporization in the pipe line, the pipe line over the bridge is laid such that it is not more than

  1. 2.4m above hydraulic gradient

  2. 6.4m above hydraulic gradient

  3. 10m above hydraulic gradient

  4. 1.4m above hydraulic gradient


Correct Option: B
Explanation:

To avoid vaporization in the pipe line, the pipe line over the bridge is laid such that it is not more than 6.4m above hydraulic gradient

A hydraulic press has a ram of 15 cm diameter and plunger is 1.5 cm. It is required to lift a weight of 1 tonne. The force required on plunger is

  1. 10kg

  2. 100 kg

  3. 1000 kg

  4. 1 kg


Correct Option: A
Explanation:

Weight on the ram  $F  =  mg=1000\times 10 = 10000$

Using Pascal's law      $\dfrac{F}{A } = constant$              where $A = \pi D^2$
$\therefore$      $\dfrac{10000}{(15)^2 } =\dfrac{F _p}{(1.5)^2}$              $\implies F _p = 100$ N $= 10\ kgf$

Thus, force required on plunger is $10\ kgf$

The maximum number of jets generally employed in an impulse turbine without jet interference are

  1. 6

  2. 5

  3. 7

  4. 8


Correct Option: A
Explanation:

The maximum number of jets generally employed in an impulse turbine without jet interference are 6.

In a typical hydraulic press, a force of 20 N is exerted on small piston of area 0.050 m2. What is force exerted by large piston on load if it has an area of 0.50 m2?

  1. 200N

  2. 100N

  3. 50N

  4. 10N


Correct Option: A
Explanation:

Using   $\dfrac{F _1}{A _1} = \dfrac{F _2}{A _2}$

$\therefore$   $\dfrac{20}{0.05} = \dfrac{F _2}{0.5}$            $\implies F _2 = 200$  N

Principle of similitude forms the basis for:

  1. comparing two identical equipments

  2. designing models so that the result can be converted to prototypes

  3. hydraulic designs

  4. performing acceptance tests


Correct Option: B
Explanation:

The principle of similitude is a supplement to the scientific method advocated by Lord Rayleigh that requires that any suggested scientific law be examined for its relationship to similar law.

This principle forms the basis for designing models so that the result can be converted to prototypes.
Hence, option B is correct.