This set of Fluid Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Kinetic Energy Correction and Momentum Correction Factors”.

1. What is the value of kinetic energy factor during a laminar flow?

a) 1

b) 2

c) 3

d) 4

View Answer

Explanation: Kinetic energy factor for a fully developed laminar flow is around 2. Laminar flow occurs when a fluid flows in parallel layers. The flow must not have any sort of disruption between the layers of fluid. The fluid flows without a lateral mixing which makes it slide past one another.

2. Which among the following is not an application of the Bernoulli?

a) Sailing

b) Flow through a venture tube

c) Flow through a sharp-edged orifice.

d) Closing of tap water

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Explanation: This is mainly because, Bernoulli’s equation is applied only when the fluid is irrotational. It means that the stream lines are not supposed to intersect each other. Also, the equation does not take viscosity into account. Thus, the flow rate decreases when you close the valve.

3. If you double the kinetic energy of an arrow, by what factor does its speed increase?

a) 2

b) 4

c) same

d) √2

View Answer

Explanation: Kinetic energy depends upon velocity and mass. The relation between K.E with mass and velocity is K.E= 0.5mv

^{2}. If we double the kinetic energy, the velocity has to be increased by a factor equal to the square root of two.

4. What is the function of Reynolds number?

a) To detect pressure changes

b) To predict flow patterns

c) Temperature

d) Viscosity

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Explanation: Reynolds number is a dimensionless quantity. It is used to predict flow patterns in different types of fluid flow. At lower Reynold’s number, the flow is laminar. At higher Reynolds number, the flow is turbulent.

5. When a bullet hits a solid block and gets embedded into it. What is conserved?

a) Momentum only

b) Kinetic energy only

c) Momentum and kinetic energy

d) Mass

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Explanation: When the bullet is released from the gun, it moves through the individual air molecules. These molecules tend to vibrate which cannot be seen though our naked eye. The solid block acts as a “momentum sink”. It’s so big when compared to a tiny bullet that it can absorb all the momentum without visibly moving.

6. If the kinetic energy is increased 4 times its initial value, then how does its momentum change?

a) 100%

b) 50%

c) 200%

d) 150%

View Answer

Explanation: Kinetic energy depends upon velocity and mass. The relation is K.E= 0.5mv

^{2}. If we increase the kinetic energy by 4 times its initial value, the momentum has to be increased by 100% its initial value.

7. When a charged body enters a uniform magnetic field. How will it’s kinetic energy change?

a) Doubles

b) 4 times

c) Constant

d) Triples

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Explanation: The kinetic energy remains a constant as the magnetic field always exerts a force perpendicular to the particle’s velocity. So, there is no change in the velocity of the fluid. Therefore, kinetic energy remains the same.

8. What is the relation between kinetic energy and momentum?

a) p=m/v

b) p=mva

c) p=mv

d) p=m

View Answer

Explanation: Kinetic energy depends upon velocity and mass. The relation is K.E= 0.5mv

^{2}. The momentum(p) of the body=mv. Now, equating the two we get, K.E=0.5mv

^{2}=p

^{2}/2m. Therefore, the relation between kinetic energy and momentum is (p=mv).

9. How can you slow down a fast neutron?

a) Applying an electric field

b) Using shield

c) Elastic collision

d) Heavy water

View Answer

Explanation: The fast neutrons are converted to thermal neutrons when they are passed through heavy water(D

_{2}O). The key factor for the neutrons to slow down are its atomic number. The velocity of the fast neutrons decreases with a few collisions.

10. If a cricket ball moves with a velocity ‘v’ and collides with a tiny table tennis ball. After an elastic collision, at what velocity will the second ball move?

a) v

b) v/2

c) 2v

d) v^{2}

View Answer

Explanation: Since the collision is elastic, the cricket ball having a higher mass than that of the tiny table tennis ball will hit and generate a higher velocity. After immediate impact, the table tennis ball will move exactly with twice the velocity of the cricket ball.

**Sanfoundry Global Education & Learning Series – Fluid Mechanics.**

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