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Mechanical Properties of Fluids — MH-CET Physics MCQs with Solutions
Free MH-CET Physics Mechanical Properties of Fluids MCQs with step-by-step solutions covering Fluid Pressure & Density, Pascal's Law & Applications, Surface Tension, Continuity Equation, Viscosity & Stokes' Law, Bernoulli's Theorem. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — Fluid Pressure & Density · easy · numerical
The gauge pressure at a depth of $10\text{ m}$ below the surface of water is ($\rho = 1000\text{ kg/m}^3$, $g = 10\text{ m/s}^2$):
A. $10^6\text{ Pa}$
B. $10^4\text{ Pa}$
C. $10^5\text{ Pa}$ ✓ Correct
D. $2 \times 10^5\text{ Pa}$
Solution: Gauge pressure is the excess over atmospheric: $P = \rho g h = 1000 \times 10 \times 10 = 10^5\text{ Pa}$, which is about one atmosphere.
Q2 — Fluid Pressure & Density · easy · theory
The pressure exerted by a liquid at a point inside it depends on:
A. The total weight of the liquid in the vessel
B. The depth of the point and the density of the liquid ✓ Correct
C. The area of the base of the vessel
D. The shape of the containing vessel
Solution: From $P = P_0 + \rho g h$, only depth and density matter. This is the hydrostatic paradox: vessels of very different shapes holding different amounts of liquid show the same pressure at the same depth.
Q3 — Fluid Pressure & Density · easy · theory
Archimedes' principle states that the buoyant force acting on a body immersed in a fluid is equal to:
A. The weight of the body
B. The weight of the fluid displaced by the body ✓ Correct
C. The volume of the fluid displaced
D. The density of the fluid times the volume of the body
Solution: The upthrust equals the weight of the displaced fluid, $F_B = V_{disp}\,\rho_{fluid}\,g$, and acts vertically upward through the centre of buoyancy.
Q4 — Fluid Pressure & Density · easy · theory
In a connected vessel containing a liquid at rest, the pressure at all points lying in the same horizontal plane is:
A. Greater in the narrower limb
B. Dependent on the cross-sectional area
C. Greater in the wider limb
D. The same ✓ Correct
Solution: Since pressure varies only with depth in a static fluid, all points at the same horizontal level in the same continuous liquid are at equal pressure, whatever the shape of the limb.
Q5 — Fluid Pressure & Density · easy · theory
The relation between absolute pressure $P_{abs}$, gauge pressure $P_g$ and atmospheric pressure $P_0$ is:
A. $P_{abs} = P_g - P_0$
B. $P_{abs} = P_g + P_0$ ✓ Correct
C. $P_{abs} = P_g \times P_0$
D. $P_{abs} = P_0 - P_g$
Solution: A gauge reads pressure relative to the atmosphere, so the true (absolute) pressure is the gauge reading plus atmospheric pressure.
Q6 — Fluid Pressure & Density · easy · theory
The SI unit of pressure is the pascal, which is equivalent to:
A. $\text{N}\cdot\text{m}$
B. $\text{N}\cdot\text{m}^2$
C. $\text{N/m}^2$ ✓ Correct
D. $\text{N/m}$
Solution: Pressure is force per unit area, so $1\text{ Pa} = 1\text{ N/m}^2$.
Q7 — Fluid Pressure & Density · easy · numerical
The pressure due to a water column at the bottom of a tank $2\text{ m}$ deep is ($\rho = 1000\text{ kg/m}^3$, $g = 9.8\text{ m/s}^2$):
A. $19600\text{ Pa}$ ✓ Correct
B. $39200\text{ Pa}$
C. $2000\text{ Pa}$
D. $9800\text{ Pa}$
Solution: $P = \rho g h = 1000 \times 9.8 \times 2 = 19600\text{ Pa}$.
Q8 — Fluid Pressure & Density · easy · theory
The relative density (specific gravity) of a substance is:
A. A dimensionless ratio with no unit ✓ Correct
B. Measured in $\text{kg/m}^3$
C. Measured in $\text{N/m}^2$
D. Measured in $\text{g/cm}^3$
Solution: Relative density is the ratio of the density of a substance to the density of water, so the units cancel and it is a pure number.
Q9 — Fluid Pressure & Density · easy · theory
A manometer is an instrument used to measure:
A. The density of a liquid
B. The surface tension of a liquid
C. The viscosity of a liquid
D. The pressure difference between a gas and the atmosphere ✓ Correct
Solution: A manometer balances the unknown pressure against a liquid column; the height difference between the limbs gives the pressure difference directly as $\rho g h$.
Q10 — Pascal's Law & Applications · easy · theory
Pascal's law states that a pressure applied to an enclosed incompressible fluid at rest is:
A. Reduced in proportion to the distance travelled
B. Transmitted undiminished to every point of the fluid and the walls ✓ Correct
C. Transmitted only along the direction of the applied force
D. Transmitted only in the downward direction
Solution: Pascal's law is the basis of all hydraulic machines: the added pressure appears equally everywhere in the enclosed fluid, regardless of direction or distance.
Q11 — Pascal's Law & Applications · easy · numerical
In a hydraulic lift, a force of $100\text{ N}$ is applied on a piston of area $0.01\text{ m}^2$. The force produced on the larger piston of area $0.5\text{ m}^2$ is:
A. $2000\text{ N}$
B. $50\text{ N}$
C. $5000\text{ N}$ ✓ Correct
D. $500\text{ N}$
Solution: Pressure is common: $\dfrac{F_1}{A_1} = \dfrac{F_2}{A_2}$, so $F_2 = 100 \times \dfrac{0.5}{0.01} = 100 \times 50 = 5000\text{ N}$.
Q12 — Pascal's Law & Applications · easy · numerical
A force of $200\text{ N}$ acts on the small piston of a hydraulic press of area $5\text{ cm}^2$. If the large piston has an area of $500\text{ cm}^2$, the force it exerts is:
A. $100000\text{ N}$
B. $20000\text{ N}$ ✓ Correct
C. $2000\text{ N}$
D. $500\text{ N}$
Solution: $F_2 = F_1 \dfrac{A_2}{A_1} = 200 \times \dfrac{500}{5} = 200 \times 100 = 20000\text{ N}$.
Q13 — Pascal's Law & Applications · easy · theory
In a hydraulic lift, the ratio of the forces on the two pistons is equal to:
A. The ratio of their volumes
B. The inverse ratio of their areas
C. The ratio of their areas ✓ Correct
D. The ratio of their radii
Solution: Since Pascal's law makes the pressure equal, $\dfrac{F_1}{A_1} = \dfrac{F_2}{A_2}$, hence $\dfrac{F_1}{F_2} = \dfrac{A_1}{A_2}$.
Q14 — Pascal's Law & Applications · easy · theory
Hydraulic brakes used in automobiles work on the principle of:
A. Stokes' law
B. Archimedes' principle
C. Bernoulli's theorem
D. Pascal's law ✓ Correct
Solution: Pressing the brake pedal raises the pressure in the brake fluid; that increase is transmitted undiminished to all the wheel cylinders, so every wheel is braked equally.
Q15 — Pascal's Law & Applications · easy · theory
Neglecting the weight of the fluid itself, the pressure at every point in an enclosed hydraulic system is:
A. Greatest at the large piston
B. Greatest at the small piston
C. Proportional to the piston area
D. The same throughout ✓ Correct
Solution: By Pascal's law the transmitted pressure is uniform. The forces differ only because the pistons have different areas, since $F = PA$.
Q16 — Pascal's Law & Applications · easy · theory
A hydraulic machine is said to multiply:
A. Neither force nor energy
B. Energy, but not force
C. Both force and energy
D. Force, but not energy ✓ Correct
Solution: Energy conservation forbids getting more work out than is put in. The machine trades distance for force: a large output force acts over a correspondingly small displacement.
Q17 — Pascal's Law & Applications · easy · theory
A dentist's chair is raised using a hydraulic system because such a system provides:
A. Complete elimination of friction in the mechanism
B. A large, smooth and uniformly distributed lifting force from a small effort ✓ Correct
C. An increase in the energy supplied to the load
D. A reduction in the total weight to be lifted
Solution: The pressure is transmitted equally in all directions, so the lift is steady and jerk-free, and the large output piston converts a modest effort into a large force.
Q18 — Continuity Equation · easy · theory
The equation of continuity for the steady flow of an incompressible fluid, $A_1 v_1 = A_2 v_2$, is a direct consequence of the conservation of:
A. Angular momentum
B. Energy
C. Momentum
D. Mass ✓ Correct
Solution: In steady flow the mass entering any section per second must equal the mass leaving it, giving $\rho A v = $ constant. For an incompressible fluid $\rho$ cancels, leaving $Av = $ constant.
Q19 — Continuity Equation · easy · theory
Water flows through a pipe whose cross-sectional area is halved at a constriction. The speed of flow at the constriction:
A. Doubles ✓ Correct
B. Halves
C. Becomes four times
D. Remains the same
Solution: By continuity $Av = $ constant, so $v \propto \dfrac{1}{A}$. Halving the area doubles the speed.
Q20 — Continuity Equation · easy · numerical
Water enters a pipe of cross-section $4\text{ cm}^2$ at $2\text{ m/s}$ and leaves through a section of area $2\text{ cm}^2$. The exit speed is:
A. $4\text{ m/s}$ ✓ Correct
B. $1\text{ m/s}$
C. $2\text{ m/s}$
D. $8\text{ m/s}$
Solution: $A_1 v_1 = A_2 v_2 \Rightarrow 4 \times 2 = 2 \times v_2 \Rightarrow v_2 = 4\text{ m/s}$.
Q21 — Continuity Equation · easy · theory
The volume flow rate of a liquid of speed $v$ through a pipe of cross-sectional area $A$ is given by:
A. $A v^2$
B. $\dfrac{v}{A}$
C. $Av$ ✓ Correct
D. $\dfrac{A}{v}$
Solution: In one second the liquid advances a distance $v$, sweeping out a cylinder of volume $Av$. Its SI unit is $\text{m}^3/\text{s}$.
Q22 — Continuity Equation · easy · numerical
Water flows at $0.02\text{ m}^3/\text{s}$ through a pipe of cross-sectional area $0.01\text{ m}^2$. The speed of flow is:
A. $0.5\text{ m/s}$
B. $0.0002\text{ m/s}$
C. $20\text{ m/s}$
D. $2\text{ m/s}$ ✓ Correct
Solution: $v = \dfrac{Q}{A} = \dfrac{0.02}{0.01} = 2\text{ m/s}$.
Q23 — Continuity Equation · easy · theory
A streamline in a flowing fluid is defined as a curve such that:
A. It separates laminar flow from turbulent flow
B. The fluid speed is constant along it
C. The fluid pressure is constant along it
D. The tangent at every point gives the direction of fluid velocity there ✓ Correct
Solution: By construction, the velocity vector of the fluid element at a point is tangential to the streamline passing through that point.
Q24 — Continuity Equation · easy · theory
The flow of a liquid through a pipe is regarded as turbulent if the Reynolds number $R_e$ is:
A. Between $1000$ and $2000$
B. Exactly zero
C. Greater than $2000$ ✓ Correct
D. Less than $1000$
Solution: Flow is laminar for $R_e < 1000$, unstable in the transition band $1000 < R_e < 2000$, and fully turbulent for $R_e > 2000$.
Q25 — Continuity Equation · easy · theory
The Reynolds number is a:
A. Quantity measured in $\text{m/s}$
B. Quantity measured in $\text{kg/m}^3$
C. Quantity measured in $\text{Pa}\cdot\text{s}$
D. Dimensionless quantity ✓ Correct
Solution: It is the ratio of inertial force to viscous force, so all dimensions cancel and it is a pure number.
Q26 — Continuity Equation · easy · theory
The critical velocity of a liquid flowing through a tube is the speed:
A. At which the viscosity becomes zero
B. At which the pressure becomes maximum
C. Above which streamline flow changes to turbulent flow ✓ Correct
D. At which the liquid stops flowing
Solution: Below the critical velocity the flow is orderly and laminar; above it the flow breaks into eddies and becomes turbulent.
Q27 — Continuity Equation · easy · theory
The mass flow rate of a fluid of density $\rho$ through a pipe of area $A$ at speed $v$ is:
A. $\dfrac{A v}{\rho}$
B. $\rho A v^2$
C. $\rho A v$ ✓ Correct
D. $\dfrac{\rho A}{v}$
Solution: Volume flow rate is $Av$, so the mass crossing a section per second is $\rho Av$, measured in $\text{kg/s}$.
Q28 — Continuity Equation · easy · theory
Water emerges faster when the nozzle of a garden hose is partially closed with a thumb because:
A. The viscosity of the water decreases
B. The pressure of the water supply increases
C. Reducing the area increases the speed, by the equation of continuity ✓ Correct
D. The density of the water decreases
Solution: The same volume per second must pass through a smaller opening, so $Av = $ constant forces the exit speed up.
Q29 — Continuity Equation · easy · theory
In the steady flow of an incompressible liquid, the product $Av$ along a tube of flow is:
A. Greatest where the tube is widest
B. Constant at every cross-section ✓ Correct
C. Proportional to the pressure
D. Greatest where the tube is narrowest
Solution: That is precisely the statement of the equation of continuity: the volume flow rate is the same through every section of the tube of flow.
Q30 — Bernoulli's Theorem · easy · theory
Bernoulli's equation for the steady flow of an ideal fluid states that the following quantity is constant along a streamline:
A. $P + \dfrac{1}{2}\rho v + \rho g h$
B. $P + \rho v^2 + \rho g h$
C. $P + \dfrac{1}{2}\rho v^2 + \rho g h$ ✓ Correct
D. $P \times \dfrac{1}{2}\rho v^2 \times \rho g h$
Solution: The three terms are the pressure energy, kinetic energy and potential energy per unit volume. Their sum is conserved along a streamline for an ideal fluid.