Most Important Fluid Dynamics MCQs | Physics MCQs

This theorem is a special case of Bernoulli's equation where the potential energy of the fluid at height h is converted into kinetic energy at the orifice.

Stokes' law for drag force depends on viscosity, not density. Density is used when calculating terminal velocity, where weight is involved.

A much larger drag force means that the balance with weight occurs at a much lower speed.

To maintain flow, blood speeds up in the narrowed region (continuity). This higher speed results in lower internal pressure, which can cause the artery to collapse or dislodge plaque.

This is the definition of viscosity. High viscosity means high resistance to flow (like honey), while low viscosity means it flows easily (like water).

Above a critical speed, the smooth, layered flow breaks down into chaotic, irregular motion.

The correct formula is Eₚ = (1/2)kx². The calculation is 0.5 × 400 × (0.2)² = 8 J.

This is the defining characteristic. A superfluid can flow without any internal friction or loss of kinetic energy.

The low pressure created by the fast air stream allows the higher atmospheric pressure on the liquid's surface in the bottle to push it up the tube.

The formula vₜ = (2ρgr²)/(9η) shows that terminal velocity is proportional to the square of the radius (r²). If r is doubled, vₜ increases by a factor of 2²=4.

This is the definition of elasticity, the ability to recover from deformation.

This is the specific region where the relationship is linear, which is the essence of Hooke's Law.

Buoyant force = (density of fluid) x (volume displaced) x g. The calculation is 1000 × 0.01 × 9.8 = 98 N.

The buoyant force, which equals the weight of the displaced fluid, must be equal to the object's total weight for it to float.

The aorta has a smaller total area (A₁) than the sum of all the branching arteries (A₂). By A₁v₁ = A₂v₂, if A₂ > A₁, then v₂ must be less than v₁.

Each term in the equation represents a form of energy per unit volume: pressure (work energy), kinetic energy, and potential energy.

The side spinning with the airflow has faster-moving air (lower pressure), while the side spinning against the airflow has slower air (higher pressure), creating a net force.

If the height does not change (h₁ = h₂), the potential energy term (ρgh) is the same on both sides of the equation and can be cancelled out.

This is the correct term for materials that can be stretched, bent, or drawn into a wire without breaking.

The buoyant force from the displaced ambient air is greater than the total weight of the balloon, which is an application of the principle of flotation.

Increased thermal energy overcomes the intermolecular cohesive forces, reducing the liquid's resistance to flow.

In gases, viscosity arises from molecular collisions. Higher temperature means more frequent and energetic collisions, which increases the resistance to flow.

Any thermal expansion or contraction will affect both wires equally, so the measurement of extension due to the load remains accurate.

High-carbon steel is hard but brittle. It will fracture soon after its elastic limit is reached, unlike more ductile low-carbon steel.

Flow rate = Area x Velocity. Therefore, Velocity = Flow rate / Area. The calculation is 2 / 0.5 = 4 m/s.

The hot, less dense smoke accelerates upwards. As its velocity increases, it crosses the threshold from laminar to turbulent flow.

The formula is v = √(2gh). The calculation is √(2 × 9.8 × 5) ≈ 9.9 m/s.

This is a classic real-world example of Bernoulli's effect. The higher pressure of the stationary air behind you pushes you into the low-pressure region created by the train.

This is the definition of an incompressible fluid – its mass per unit volume does not change under pressure.

Pressure is force per unit area. In the context of the energy equation, it represents the work done on or by the fluid element per unit volume.

This is the correct definition of plastic deformation, occurring after the elastic limit has been exceeded.

An ideal fluid flow must conserve both mass (continuity) and energy (Bernoulli), so both equations must be satisfied.

This is the fundamental reason for lift, as explained by Bernoulli's principle.

The upward buoyant force counteracts some of the downward gravitational force, resulting in a lower apparent weight.

Wool is a natural polymer, composed of long-chain protein molecules.

This is the name given to the principle that an increase in a fluid's speed occurs simultaneously with a decrease in pressure.

A fast jet of oxygen creates a low-pressure zone that entrains a predictable amount of ambient air, which is an application of Bernoulli's principle.

Shear stress involves forces applied parallel to a surface, causing one layer of the material to slide relative to another, thus changing its shape.

Young's modulus is the ratio of stress (in Pascals) to strain (dimensionless). Therefore, its units are the same as stress, Pascals (Pa) or N/m².

In physics, 'elasticity' refers to the ability to resist deformation. Steel has a very high Young's Modulus, making it extremely elastic.

The cross-sectional area A = πr². If r becomes r/2, the new area becomes A/4. To keep Av constant, v must increase by a factor of 4.

This is the correct definition, as used in Torricelli's theorem for the 'speed of efflux'.

Mass is proportional to volume, and volume is proportional to r³. If mass increases by a factor of 8, the radius must have increased by a factor of ³√8 = 2.

The inverted wing shape creates higher pressure on top and lower pressure underneath, pushing the car onto the track.

All real fluids possess some viscosity (internal friction) and are compressible to some extent, unlike ideal fluids.

According to Hooke's Law, F = kx. Therefore, k = F/x = 10 N / 0.05 m = 200 N/m.

This is a direct application of Bernoulli's principle for a horizontal pipe.

This is the correct term for the branch of physics concerned with fluids in motion.

A screw gauge (or micrometer) is designed to measure very small dimensions like the diameter of a wire with high precision.

UTS is the peak of the stress-strain curve, after which the material begins to 'neck' and weaken.

This is the definition of a streamline; it shows the instantaneous direction of flow at every point.

Drag is a surface force caused by interaction with the fluid; it does not depend directly on the mass of the object.

Terminal velocity is proportional to the square of the radius. A larger radius means a significantly higher terminal velocity.

Hydraulic brakes operate on Pascal's law, which relates to pressure in a confined, static fluid.

Cohesion is the attraction between like molecules, responsible for holding a substance together.

From Y = (FL)/(AΔL), we get F = (YAΔL)/L. The new area is A' = π(2r)² = 4A. The new length is L' = 2L. So, F' = (Y(4A)ΔL)/(2L) = 2 * (YAΔL)/L = 2F.

These are the three main assumptions made to define an ideal fluid, which simplifies the analysis of fluid dynamics.

In the narrower section, the fluid must speed up. Denser streamlines are used to visually represent regions of higher velocity.

For a sphere moving under laminar conditions, the constant of proportionality is 6π.

The fast-moving air you blow over the top of the paper creates a low-pressure zone, and the higher pressure of the still air underneath pushes the paper up.

This is the correct term for when the force of gravity is balanced by the drag force, resulting in zero acceleration and constant velocity.

The poise (and the more common centipoise) is a CGS unit of dynamic viscosity.

This is the correct term for the ability of a substance, especially a metal, to be deformed or molded into a different shape.

The work done against the elastic restoring force is stored as potential energy.

The formula for hydrostatic pressure is P = ρgh, where ρ is the fluid density.

Since kinetic energy is (1/2)mv² and density ρ = m/V, then (1/2)ρv² equals KE/V.

As the water accelerates due to gravity (v increases), its cross-sectional area (A) must decrease to keep the flow rate (Av) constant.

The combination of the ball's spin and its travel through the air creates a pressure differential that pushes it to one side.

At terminal velocity, the drag force has grown to be equal in magnitude to the weight, so the two forces balance and the net force is zero.

A barometer is a static device that measures existing atmospheric pressure; it does not involve fluid flow to operate.

Strain = Stress / Young's Modulus. The calculation is (4 × 10⁸) / (200 × 10⁹) = 0.002.

Polymers consist of long chains that can have both ordered (crystalline) and disordered (amorphous) regions.

For an object to float, it must be less dense on average than the fluid it is in.

The fast-moving wind creates a low-pressure zone according to Bernoulli's principle, which enhances the draft.

This is the correct term for chaotic, unpredictable fluid motion.

Viscosity (η) is in the denominator of the equation, meaning that as the fluid's viscosity increases, the terminal velocity decreases.