This set of Fluid Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Shear Stress and Pressure Gradient”.

1. What is the unit of shear stress?

a) N/m^{3}

b) N/mm^{3}

c) N/m

d) Pascal

View Answer

Explanation: Shear stress is defined as the force acting per unit area. Thus, the unit of shear stress is equal to N/m

^{2}. Since, 1 Pa =1 N/m

^{2}, Pascal is the most suitable one.

2. Shear stress is caused due to _______

a) Friction

b) Temperature

c) Pressure

d) Volume

View Answer

Explanation: Shear stress is caused due to friction between fluid particles. It is formed due to the presence of fluid viscosity. Shear stress arises from the force vector component which is parallel to the cross section.

3. Which among the following is a formula for shear stress?

a) τ = F*A

b) τ = F/A

c) τ = F/m

d) τ = F*m

View Answer

Explanation: Shear stress is defined as the force acting per unit area. Shear stresses arise from shear components(forces), which are pairs of equal and opposite forces. These forces act on the opposite side of the object.

4. Which among the following is the correct formula to find out the shear modulus(G)?

a) E/2

b) v/2

c) E/2(1+v)

d) 2E(1+v)

View Answer

Explanation: Shear modulus is also called as modulus of rigidity. It is defined as the ratio of shear stress to shear strain. Since Young modulus is equal to stress by strain. The most suitable option is option c. (E= Young’s Modulus, v= poison’s ratio)

5. Which among the following is an assumption of Hagen-Poiseuille equation?

a) Fluid is compressible

b) Fluid is uniform

c) Fluid is laminar

d) Fluid is turbulent

View Answer

Explanation: Fluid flow is laminar as it is assumed to be incompressible and Newtonian. The flow is laminar through the pipe of constant cross section. Thus, there is no acceleration of fluid in the pipe. Therefore, Hagen-Poiseuille assumed that fluid flow is laminar.

6. What is the unit of pressure gradient?

a) Pa/m

b) Nm

c) Pa

d) N/m

View Answer

Explanation: Pressure gradient is a dimensional quantity. It is expressed in units of pressure per unit length. It determines which quantity and which direction the pressure changes around a particular location.

7. Which of the following is not a basic type of stress?

a) Volumetric stress

b) Shear stress

c) Compressive stress

d) Tensile stress

View Answer

Explanation: Volumetric stress is not a basic classification among the type of stresses as it describes the tendency of an object to deform in all directions. It deforms when the load acts uniformly in all directions.

8. What type of force does a stress produce?

a) Radial force

b) External force

c) Internal resistive force

d) Axial force

View Answer

Explanation: According to the continuum mechanics, stress is a physical quantity that produces internal forces. For example: When a solid bar supports a weight, each particle of the bar pushes the particles immediately below it. This happens due to the internal resistive force that is developed due to the stress on the body.

9. Hooke’s law is applicable within what limit?

a) Fracture point

b) Elastic limit

c) Ultimate strength

d) Plastic limit

View Answer

Explanation: Hooke’s law states that force is directly proportional to its extension. Hooke’s law is applicable within the elastic limit, when the body is deformed. Example: plucking the strings of a guitar.

10. Define Factor of safety

a) Ultimate stress/Permissible stress

b) Ultimate stress/ Shear stress

c) Compressive stress/ Ultimate stress

d) Tensile stress/Shear stress

View Answer

Explanation: Factor of safety determines the maximum load carrying capacity. It tells us how much stronger the system is than it usually needs to be for a particular specified load. It is the ratio of allowable stress to the actual stress.

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