# KPK 11th Class Physics Chapter 6 Fluid Dynamics Short Questions Answers

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Class/Subject: 11th Class Physics

Chapter Name: Fluid Dynamics

Board: All KPK  Boards

• Malakand Board 11th Class Physics Chapter 6 Fluid Dynamics short questions Answer
• Mardan Board 11th Class Physics Chapter 6 Fluid Dynamics short questions Answer
• Peshawar Board 11th Class Physics Chapter 6 Fluid Dynamics short questions Answer
• Swat Board 11th Class Physics Chapter 6 Fluid Dynamics short questions Answer
• Dera Ismail Khan Board 11th Class Physics Chapter 6 Fluid Dynamics short questions Answer
• Kohat Board 11th Class Physics Chapter 6 Fluid Dynamics short questions Answer
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## KPK 11th Class Physics Chapter 6 Fluid Dynamics Short Questions Answers

Smoke rises in a chimney faster when a breeze is blowing. Use Bernoulli,s principle to explain this phenomena?

Smoke rises in a chimney faster when a breeze is blowing. The Bernoulli’s principle plays a vital role in this process. As the wind blows across the top of a chimney, the pressure is less there than the pressure inside the house. Thus air and smoke are pushed up the chimney faster when a breeze is blowing.

Why do many trailer trucks use wind deflectors on the top of their cabs? How do such device reduce fuel consumption?

Many trailer trucks use wind deflectors on the top of their cabs to reduce air resistance. Using these deflectors, the work done against air resistance is reduced significantly. In this way, the consumption of fuel is minimized.

Consider the cross section of the wing on an aeroplane. The wing is designed such that the air travels faster over the tap than under the bottom. Explain why there is a net upward (lift) force on the wing due to the Bernoulli’s effect?

The wing of an aeroplane is design in such a way that the velocity of the air flow is higher about its surface as compared to its lower surface. According to Bernoulli’s principle, the pressure of a fluid decreases in the region where the speed of air is higher. Therefore, the pressure below the wing is greater due to lower velocity of air and pressure is smaller above the wing due to grater velocity of air. In this way, a pressure difference is developed which courses a net upwards (lift) force acting on the wing of aeroplane.

When a fast –moving train passes a man standing on the platform at rest. He is likely to be drawn towards train. How does the Bernoulli effect explain this phenomenon?

When a fast moving train passes a man standing on the platform at rest, the air b/w train and person also moves with greater speed. According to Bernounlli’s principle, the pressure decreases in the region where the air is flowing with higher speed. During this time, the pressure behind the person is maximum which may push him towards the low pressure region i.e. towards the train.

It you hold a sheet of paper and blow across the top surface, the paper rises. Explain?

When we blow over the top surface of the sheet of paper, the speed of air increases at the top. According to Bernoulli’s principle, the pressure decrease in the region where air flows with higher speed. Thus the pressure at the top of sheet of paper is minimum while below the sheet, the pressure is maximum. Thus difference in pressure provides a net upwards force due to which the sheet of paper rises up in the air.

If you suddenly turn on your shower water at full speed, why is the shower curtain pushed inwards?

When we turn on our shower water at full speed, the water from inside flows out at high speed. According to Bernoulli’s principle, the pressure decreases in the region where the pressure inside decrease and as a result the shower curtain is pushed inwards due to outside maximum pressure.

If air from a hair dryer is blown over the top of a ping-pong ball, can be suspended in air. Explain how the ball can remain in equilibrium?

When air blown from a hair dryer over the top of a ping-pong ball, the speed of air above the ball increases.

According to Bernoulli,s principle, the pressure decreases in the region where speed of air increases. Thus the pressure of air above the ball is reduced while the pressure below the bell is maximum. In this way, a difference in pressure is developed which provides an upward force due to which the ball is prevented from falling and thus remains in state of equilibrium.

A base ball moves past an observer from left to right spinning counterelock wise. In which direction will the ball tend to deflect?

When a fast moving base ball moves in such a way that it spins as well as moves forward, the velocity of ball increases due to spin due to which the pressure in that region decreases. While the pressure on the other side of the ball is maximum due to which the is deflected from its path. In this way, an extra curvature is given to the ball which is known as swing.

A spherical body is dropped in two different fluid and its terminal velocity is found to be different. Gives the reason?

We know that, when a spherical body of mass ‘m’ radium ‘r’ and density ‘s’ then its terminal velocity is given by,

VT=2ϑgr29ϑ   ____________ (1)

Eq (1) show that the terminal velocity of the spherical body depends upon the viscosity of the fluids. As different fluids have different viscosities, so according to eq (1) the terminal velocities of the body will be different.

A liquid passed through a pipe and it was found that the rate influx was equal to the rate of efflux. What do you get about the liquid?

When a liquid pass through a pipe and its rate of influx is equal to the rate of efflux, then such liquid have steady state flow. The liquid will be incompressible band will have uniform density.

An incompressible liquid is passed through a horizontal pipe and it was observed that the speed of a mass of liquid when emerges is greater than its speed when it enters the pipe. How can it be possible?

According to Equation of continuity,

We have,

A1   =  A2V2      => V2    A1V1/A2 ______(1)

Eq (1) shows that the speed of

A liquid emerging out from a pipe is inversely proportional to the area of cross-section of the pipe at the end through which the liquid is flowing out. So if an incompressible liquid is passed through a horizontal pipe and its speed of flow is greater than its speed of entering the pipe, then it means that the area of cross-section ‘As’ for the emergent liquids is less than the area of cross-section for the entering liquid. i,e A3< A1

Why does the pipe of paper squeezes when air is blow through it?

When air is blown through a pipe of paper, the velocity of air inside the pipe increases. According to Bernoulli,s principle, when the velocity of a fluid increases, then the pressure in that region decreases. The higher pressure of the surrounding air causes the pipe of paper to squeegee.

When water falls from a tap, its cross-sectional area decrease as it comes down Explain why?

We know that the speed of a fluid is inversely proportional to the area of cross-section. So when water causes a decrease in its area of cross-section. i,e the stream of water becomes more and more narrower [thin] as it fall down.

Why a car has oblong shape design ?

A car has oblong shape design to reduce the air resistance during motion of the car. Due to this special shape, the car faces less air friction and thus it gain high speed with consumption of less amount of fuel.

It is often seen that leaves lying on the road starts following the fast moving car when it passes through the roads. Why?

When a fast moving car passes on the road, the air adjacent to the car moves at a high speed. According to Bernoulli’s principle, when the speed of air increases, the pressure in that region is reduced. The pressure of the surrounding air is maximum and thus the surrounding air rushed to this region. This air causes the motion of the leaves lying on the road towards the fast moving car.

How do the pulsations in pulse show the heart beat?

Pulsation mean the charge in blood pressure the vessels when the heart pumps the blood in the vessels, the pressure of blood in the vessels varies accordingly. The increase in pressure inflates the vessel and the decrease in pressure squeezes the vessels. These changes in the pressure can be felt in the form of pulsations in the pulse which is equal to the heart beat i.e.

Number of pulsation = number of heart beats

Describe the working of an engine carburetor and point spray?

A) Working of engine carburetor:

The principle of engine carburetor is the same as that of filter pump. The carburetor of an engine, uses the Bernoulli’s theorem to feed a suitable amount of mixture of air and fuel to the cylinder. The engine draws air through a horizontal pipe to the cylinder. This pipe is connected to the fuel tank by a side tube. When the air through the pipe is flowing high speed, the pressure  of air inside the pipe decreases. As a result, the duel moves to the pipe and a proper mixture of the fuel vapours and air is formed which is then sprayed to the engine.

1. b) Working of point spray:

the point spray machine works on the principle of Bernoulli’s theorem. When the spray machine is pushed, the air pressure about the surface of the liquid inside the spray machine increases. As a result the liquid is forced to move up in a vertical pipe inside the liquid. the liquid emerges out through a nozzle haring very small area of cross section with high speed.

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