ETEA / KMU MDCAT (KPK) Physics Fluid Dynamics — Set 2

ETEA / KMU MDCAT (KPK) Physics Fluid Dynamics — Set 2

1. Question 1

   Q1. Water flows through a hose with a velocity of 2 m/s. If the hose's cross-sectional area is halved, what is the new velocity?

   • A) 1 m/s
   • B) 4 m/s
   • C) 2 m/s
   • D) 8 m/s

   Answer: 4 m/s

   Explanation: By the equation of continuity, velocity doubles when area is halved. Option A is incorrect because it violates this principle.

2. Question 2

   Q2. The SI unit of viscosity is

   • A) Poiseuille
   • B) Pascal-second
   • C) Newton-meter
   • D) Joule-second

   Answer: Pascal-second

   Explanation: Viscosity is measured in Pascal-seconds (Pa·s). Option A, Poiseuille, is also a unit of viscosity but not the SI unit.

3. Question 3

   Q3. Bernoulli's principle is based on the conservation of

   • A) Mass
   • B) Energy
   • C) Momentum
   • D) Charge

   Answer: Energy

   Explanation: Bernoulli's principle relates the pressure of a fluid to its velocity, based on energy conservation. Option A is related to the equation of continuity.

4. Question 4

   Q4. The flow of fluid becomes turbulent when the Reynolds number exceeds

   • A) 1000
   • B) 2000
   • C) 3000
   • D) 4000

   Answer: 2000

   Explanation: Turbulent flow typically occurs when the Reynolds number exceeds 2000-3000. Option A is too low for turbulence.

5. Question 5

   Q5. What is the primary cause of the lift force experienced by an airplane wing?

   • A) Wing shape deflecting air downward
   • B) Wing angle creating turbulence
   • C) Air viscosity
   • D) Air density

   Answer: Wing shape deflecting air downward

   Explanation: The shape of the wing deflects air downward, creating an upward lift force according to Newton's third law. Option B is incorrect as turbulence is not the primary cause.

6. Question 6

   Q6. The pressure at a point in a static fluid is given by

   • A) ρgh
   • B) ρg/h
   • C) P + ρgh
   • D) P0 + ρgh

   Answer: P0 + ρgh

   Explanation: The pressure at a point in a static fluid is given by P0 + ρgh, where P0 is atmospheric pressure. Option C is incorrect as it doesn't account for atmospheric pressure correctly.

7. Question 7

   Q7. A fluid's velocity profile is parabolic in

   • A) Turbulent flow
   • B) Laminar flow
   • C) Steady flow
   • D) Irrotational flow

   Answer: Laminar flow

   Explanation: In laminar flow, the velocity profile is parabolic due to viscous forces. Option A is incorrect because turbulent flow has a chaotic velocity profile.

8. Question 8

   Q8. The terminal velocity of a sphere falling in a viscous fluid is directly proportional to

   • A) The square of its radius
   • B) The square of its density
   • C) The fluid's viscosity
   • D) The gravitational acceleration

   Answer: The square of its radius

   Explanation: Terminal velocity is proportional to the square of the sphere's radius according to Stokes' law. Option C is incorrect because terminal velocity is inversely proportional to viscosity.

9. Question 9

   Q9. The flow rate through a pipe is given by the

   • A) Equation of continuity
   • B) Bernoulli's equation
   • C) Hagen-Poiseuille equation
   • D) Torricelli's theorem

   Answer: Hagen-Poiseuille equation

   Explanation: The Hagen-Poiseuille equation gives the flow rate through a cylindrical pipe. Option B is incorrect because Bernoulli's equation relates pressure and velocity.

10. Question 10

    Q10. The SI unit of flow rate is

    • A) m³/s
    • B) m/s
    • C) m²/s
    • D) kg/s

    Answer: m³/s

    Explanation: Flow rate is measured in cubic meters per second (m³/s). Option B is the unit of velocity.

11. Question 11

    Q11. A Pitot tube is used to measure

    • A) Fluid velocity
    • B) Fluid pressure
    • C) Fluid density
    • D) Fluid viscosity

    Answer: Fluid velocity

    Explanation: A Pitot tube measures the dynamic pressure of a fluid, which is related to its velocity. Option B is incorrect because while it involves pressure, it's used to find velocity.

12. Question 12

    Q12. The drag force on an object moving through a fluid is proportional to

    • A) Its velocity
    • B) The square of its velocity
    • C) Its acceleration
    • D) The fluid's density

    Answer: The square of its velocity

    Explanation: For turbulent flow, the drag force is proportional to the square of the velocity. Option A is incorrect because it's true for laminar flow, not generally.

13. Question 13

    Q13. Venturi meter is based on the principle of

    • A) Bernoulli's equation
    • B) Equation of continuity
    • C) Torricelli's theorem
    • D) Stokes' law

    Answer: Bernoulli's equation

    Explanation: A Venturi meter measures flow rate using the principle of Bernoulli's equation. Option B is related but not the primary principle used.

14. Question 14

    Q14. The viscosity of a fluid generally

    • A) Increases with temperature
    • B) Decreases with temperature
    • C) Remains constant with temperature
    • D) Is independent of temperature

    Answer: Decreases with temperature

    Explanation: For liquids, viscosity decreases with increasing temperature. Option A is incorrect because it's true for gases.

15. Question 15

    Q15. The flow of an ideal fluid is

    • A) Irrotational and compressible
    • B) Rotational and incompressible
    • C) Irrotational and incompressible
    • D) Rotational and compressible

    Answer: Irrotational and incompressible

    Explanation: Ideal fluid flow is assumed to be both irrotational and incompressible. Option A is incorrect because ideal fluids are incompressible.

16. Question 16

    Q16. The pressure difference between two points in a fluid at rest is given by

    • A) ρg(h1 - h2)
    • B) ρg(h2 - h1)
    • C) ρg(h1 + h2)
    • D) ρg(h2 / h1)

    Answer: ρg(h1 - h2)

    Explanation: The pressure difference is given by ρg times the height difference. Option B is incorrect because it reverses the height difference.

17. Question 17

    Q17. Torricelli's theorem states that the velocity of efflux is

    • A) √(2gh)
    • B) √(gh)
    • C) 2gh
    • D) gh

    Answer: √(2gh)

    Explanation: Torricelli's theorem states that the velocity of efflux is √(2gh), similar to free fall. Option B is incorrect because it misses the factor of 2.

18. Question 18

    Q18. The capillary rise of a liquid is inversely proportional to

    • A) The radius of the tube
    • B) The density of the liquid
    • C) The surface tension of the liquid
    • D) The angle of contact

    Answer: The radius of the tube

    Explanation: Capillary rise is inversely proportional to the radius of the tube according to Jurin's law. Option B is incorrect because it's directly related to the density.

19. Question 19

    Q19. The concept of streamlines is used to visualize

    • A) Turbulent flow
    • B) Laminar flow
    • C) Steady flow
    • D) Unsteady flow

    Answer: Steady flow

    Explanation: Streamlines are used to visualize steady flow. Option B is related but laminar flow can be either steady or unsteady.

20. Question 20

    Q20. A tank is filled with water to a height of 1.5 m. What is the pressure at the bottom of the tank?

    • A) 1.47 x 10^4 Pa
    • B) 1.50 x 10^4 Pa
    • C) 1.47 x 10^5 Pa
    • D) 1.50 x 10^5 Pa

    Answer: 1.47 x 10^5 Pa

    Explanation: Pressure = ρgh = 1000 kg/m³ * 9.8 m/s² * 1.5 m = 1.47 x 10^4 Pa; correct unit is Pa, not kPa.