Mechanical Properties of Fluids - Online Test

Q1. The stream line in a flow is
Answer : Option A
Explaination / Solution:

Streamlines, streaklines and pathlines are field lines in a fluid flow. They differ only when the flow changes with time, that is, when the flow is not steady. Considering a velocity vector field in three-dimensional space in the framework of continuum mechanics, we have that:

Streamlines are a family of curves that are instantaneously tangent to the velocity vector of the flow. These show the direction in which a massless fluid element will travel at any point in time

A streamline is one that drawn is tangential to the velocity vector at every point in the flow at a given instant and forms a powerful tool in understanding flows. This definition leads to the equation for streamlines.
where u,v, and w are the velocity components in x, y and z directions respectively as sketched.



Q2. Flow is said to be steady if
Answer : Option A
Explaination / Solution:

The flow velocity u of a fluid is a vector field 

which gives the velocity of an element of fluid at a position x and time t.

The flow of a fluid is said to be steady if u does not vary with time. That is if 


Q3. If a pipe carrying incompressible liquid has an area  and velocity  at one point  and  at another point, the equation of continuity gives the relation
Answer : Option A
Explaination / Solution:

When a fluid is in motion, it must move in such a way that mass is conserved.Consider the steady flow of fluid through a duct (that is, the inlet and outlet flows do not vary with time). The inflow and outflow are one-dimensional, so that the velocity V and density  are constant over the area A.

Now we apply the principle of mass conservation. Since there is no flow through the side walls of the duct, what mass comes in over goes out of , (the flow is steady so that there is no mass accumulation). Over a short time interval 

As volume is same so this equation can be written as 


This is a statement of the principle of mass conservation for a steady, one-dimensional flow, with one inlet and one outlet. This equation is called the continuity equation for steady one-dimensional flow.


Q4. in laminar flow
Answer : Option C
Explaination / Solution:

laminar flow (or streamline flow) occurs when a fluid flows in parallel layers, with no disruption between the layers. At low velocities, the fluid tends to flow without lateral mixing, and adjacent layers slide past one another like playing cards.

Q5. At large flow velocities the flow of a fluid becomes
Answer : Option B
Explaination / Solution:

When any liquid is flowing more than the velocity of it's critical velocity then flow becomes turbulent.

Q6. According to Bernoulli’s equation for a varying cross-section pipe carrying incompressible liquid, pressure p, density ρ velocity v and height h at a place where acceleration due to gravity is g
Answer : Option B
Explaination / Solution:

According to conservation of enegy, Total energy of any system is always conserved. And Bernoulli's Theorem says that at any point of the pipe in which the liquid is flowing the sum of all the energies (Pressure Energy,Kinetic Energy,Potential Energy) is always constant.

Q7. If a ball is spinning in an airflow it develops pressure difference between the lower and upper faces due differences in the
Answer : Option A
Explaination / Solution:

The Magnus effect is an observable phenomenon that is commonly associated with a spinning object that drags air faster around one side, creating a difference in pressure that moves it in the direction of the lower-pressure side. The Magnus effect often occurs when a spinning sphere (or cylinder) curves away from its principal flight path. This phenomenon is important in the study of the physics of many ball sports. It is also an important factor in the study of the effects of spinning on guided missiles—and has some engineering uses, for instance in the design of rotor ships and Flettner aeroplanes.

Q8. The lift on an aircraft wing arises because of
Answer : Option C
Explaination / Solution:

This is the application of Bernoulli's Theorem. If air speeds up the pressure is lowered.Thus,a wing generates lift because the air goes faster over the top creating a region of low pressure,and thus lift.

Q9. The lift on an aircraft wing arises because of
Answer : Option C
Explaination / Solution:

This is the application of Bernoulli's Theorem. If air speeds up the pressure is lowered.Thus,a wing generates lift because the air goes faster over the top creating a region of low pressure,and thus lift.

Q10. The coefficient of viscosity for a fluid is defined as the ratio of
Answer : Option D
Explaination / Solution:

The degree to which a fluid resists flow under an applied force, expressed as the ratio of the shearing stress to the velocity gradient. The coefficient of viscosity of liquids decreases as temperature increases because the bonds between molecules are weakened.