Properties of Fluid MCQs – Part 2

Question 16Easy

A real fluid, in which the shear stress is NOT proportional to the rate of shear strain is called:

Answer: D. Non-Newtonian fluid

A fluid whose shear stress is not directly proportional to the rate of shear strain is called a non-Newtonian fluid.

Question 17Easy

The coefficient of viscosity (μ) is the resisting property of a fluid to shearing force. The units of dynamic viscosity are Pa-s and poise. What is the relation between poise and Pa-s?

Full explanation

Answer: D. 1 poise = 1/10 Pa-s

1 poise is 1 dyne·s/cm², which equals exactly 0.1 Pa·s (1/10 Pa·s).

Question 18Easy

Two liters of a petrol having specific gravity 0.805 weigh 15.8 N. Calculate its density in kg/m³.

Full explanation

Answer: C. 805

Density of petrol is its specific gravity multiplied by the density of water: ρ = 0.805 × 1000 = 805 kg/m³.

Question 19Easy

Specific gravity of a fluid is the ratio of its density to the density of a well-known fluid. Compare the specific gravity of water, mercury and oil. Take S_w = specific gravity of water, S_oil = specific gravity of oil, and S_M = specific gravity of mercury.

Full explanation

Answer: C. S_M > S_W > S_oil

Mercury has specific gravity ≈ 13.6, water is 1.0, and oils typically range from 0.8 to 0.9, so S_M > S_W > S_oil.

Question 20Easy

The phenomenon of rise or fall of liquid level in a capillarity tube is called as capillarity. In non-wetting liquids (e.g. mercury), what is the relation between cohesion of mercury and adhesion between mercury and capillary tube?

Full explanation

Answer: A. Cohesion is greater than adhesion

In non-wetting liquids like mercury, cohesive forces between liquid molecules exceed adhesive forces with the tube wall, resulting in capillary depression.

Question 21Easy

Two litres of an oil weight 16 N. Calculate the specific gravity of the oil. Take density of water as 998 kg/m³.

Full explanation

Answer: C. 0.816

Oil density is 16 N / (9.81 × 0.002 m³) ≈ 815.49 kg/m³. Specific gravity is 815.49 / 998 ≈ 0.816.

Question 22Easy

The reciprocal of density is known as specific volume. The dimension of specific volume of a fluid is:

Full explanation

Answer: C. M⁻¹ L³

Specific volume is volume per unit mass: [L³] / [M] = [M⁻¹ L³] (or [M⁻¹ L³ T⁰]).

Question 23Easy

Density of a fluid is its mass per unit volume. The dimension of density of a fluid is:

Full explanation

Answer: C. M L⁻³

Density is mass per unit volume: [M] / [L³] = [M L⁻³].

Question 24Easy

The surface of a liquid acts like a stretched elastic membrane under tension. This is mainly due to:

Full explanation

Answer: C. surface tension

Surface tension causes the free liquid surface to contract and act like a stretched elastic membrane under tension.

Question 25Medium

A plate at a distance of 0.03 mm from a fixed plate moves at 0.8 m/s and requires a force of 1.50 N/m² area of plate. Determine the dynamic viscosity of liquid between the plates.

Full explanation

Answer: A. 56.25 × 10⁻⁶ N·s/m²

Using τ = μ(du/dy), μ = τ × dy / du = 1.50 × (0.03 × 10⁻³) / 0.8 = 56.25 × 10⁻⁶ N·s/m².

Question 26Easy

A real fluid in which the shear stress is directly proportional to the velocity gradient is known as:

Full explanation

Answer: B. Newtonian fluid

A fluid in which shear stress is directly proportional to the velocity gradient (rate of shear strain) is a Newtonian fluid.

Question 27Easy

What is the SI unit for dynamic viscosity?

Full explanation

Answer: A. Pascal second

The SI unit of dynamic viscosity is the Pascal second (Pa·s), which is equivalent to N·s/m² or kg/(m·s).

Question 28Easy

Match the items in List 1 (name of quantities) with those in List 2 (units of quantities in the SI system): M. Dynamic viscosity, N. Kinematic viscosity, O. Surface tension, P. Energy.

Full explanation

Answer: B. M-3, N-4, O-1, P-2

Dynamic viscosity is N·s/m² (3), kinematic viscosity is m²/s (4), surface tension is N/m (1), and energy is N·m (2): M-3, N-4, O-1, P-2.

Question 29Easy

A fluid in which shear stress is more than the yield value and is proportional to rate of shear strain is known as:

Full explanation

Answer: C. ideal plastic fluid

A fluid that requires an initial yield stress before flowing, after which shear stress varies linearly with shear rate, is an ideal plastic (Bingham plastic).

Question 30Easy

What is the shear stress of fluid at rest?

Full explanation

Answer: B. Zero

A fluid at rest cannot sustain any shear force; because the velocity gradient du/dy is zero, the shear stress is strictly zero.