Define average pressure.Mention it's unit or a vector? and dimensional f... | Physics

MECHANICAL PROPERTIES OF FLUIDS

Very Short Question Answers

Q1. Define average pressure.Mention it's unit or a vector? and dimensional formula. Is it a scalar
Ans.

Average pressure: The normal force acting per unit area is known as average pressure.Pressure is a scalar quantity

$Average \: pressure\,\, P_{av}=\frac{F}{A}$

S.I Unit- $Pascal$ ,(or) $N/\,m^{2}$ Dimensional Formula :$\,\,[M^{1}\,L^{-1}\,T^{-2}\,]$

Q2. Defile Viscosity. What are it's units and dimensions?
Ans.

Viscosity: TThe frictional force which opposes the relative motion between the layers of a fluid.(or) The resistance to the fluid motion

S.I Unit- $Poiseuille$ , $Pa\,s$ Dimensional Formula :$\,\,[M^{1}\,L^{-1}\,T^{-1}\,]$

Q3. What is the principle behind the carburetor of an automobile?
Ans.

Bernoulli’s principle

Q4. What is magnus effect?
Ans.

When the spinning ball is in air fluid the dynamic lift due to spinning is called Magnus effect.

Q5. Why are drops and bubbles spherical?
Ans.

Due to surface tension (or) To acquire minimum surface area

Q6. Give the expression for the excess pressure in a liquid drop.
Ans.

Pressure $P=\frac{2T}{R}$
T= surface tension, r = radius.

Q7. Give the expression for the excess pressure in an air bubble inside the liquid.
Ans.

Pressure $P=\frac{2T}{R}$
T= surface tension, r = radius.

Q8. Give the expression for the soap bubble in air.
Ans.

Pressure $P=\frac{4T}{R}$

T= surface tension, r = radius.

Q9. What are water proofing agents and water wetting agents?What do they do?
Ans.

The material when applied on the surface of solid increase the angle of contact with the liquid is called water proofing agents.
The material when mixed with liquid decreases the angle of contact with the given solid actually made acute is called wetting agent.

Q10. What is angle of contact?
Ans.

The angle between tangent to the liquid surface at the point of contact and solid surface inside the liquid is called angle of contact.
The angle of contact for mercury = 140°, pure water = 0°

Q11. Mention any two examples that Obey Bernoullis theorem and justify ththem.
Ans.

In heavy winds house roofs are blown off. When the velocity is greater on the roof top then inside the house, the pressure on the roof top becomes less than that inside the house.This pressure differences.Causes dynamic lift and hence the roof is blown off.
When fan is rotating, papers are blown off from the table top. The velocity of wind on the paper increases due to fan and hence pressure decreases. It lifts it is blown to a side.
Dynamic lift on an Aeroplan wing.
Magnus effect.

Q12. When water flows through a pipe, which of the layers moves fastest and slowest ?
Ans.

The water layer which moves along the axis of the pipe is fastest.

The water layer which is in contact with the pipe moves slowest.

Q13. Terminal velocity is more if surface area of the body is more. Give reasons in support of your answer.
Ans.

According to stokes law, the terminal velocity $V_{t}\propto r^{2} $, area $A= 4\pi r^{2} $

$\therefore V_{t}\propto r^{2} $ , So,terminal velocity is more is more if surface area of the body is more