# Engineering Physics Questions and Answers – Streamline and Turbulent Flow

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This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Streamline and Turbulent Flow”.

1. A metal plate 5cm×5cm rest on a layer of castor oil 1mm thick whose coefficient of viscosity is 1.55Nsm(-2). Find the horizontal force required to move the plate with a speed of 2 cms(-1).
a) 0.775N
b) 0.0577N
c) 0.0775N
d) 0.577N

Explanation: F=ȠA dv/dx
F=1.55×25×10-4×(2×10-2)/(1×10-3)=0.0775N.

2. At what speed will the velocity head of stream of water be 40 cm?
a) 2.80cms-1
b) 280 cms-1
c) 28 cms-1
d) 0.280 cms-1

Explanation: h=v2/2g
v=√2gh=√(2×980×40)=280cms-1.

3. It is easier to cut an apple with a blunt knife than a sharp knife.
a) True
b) False

Explanation: The area of a sharp edge is much less than the area of a blunt edge. For the same total force, the effective force per unit area is more for the sharp edge than the blunt one. Hence a sharp knife cuts easily than a blunt knife.

4. It is easier to swim in sea water than in river water.
a) True
b) False

Explanation: The sea water has many salts dissolved in it. So the density of sea water is greater than that of river water. Consequently, the sea water exerts greater upthrust on the swimmer than the river water. Hence it is easier to swim in sea water than in river water.

5. If there were no gravity, which of the following will not be there for a fluid?
a) Viscosity
b) Surface tension
c) Pressure
d) Archimedes’ upward thrust

Explanation: Archimedes’ upward thrust will be absent for a fluid if there were no gravity.

6. Motion of a liquid in a tube is best described by ___________
a) Bernoulli theorem
b) Poiseuille’s equation
c) Stoke’s law
d) Archimedes’ principle

Explanation: Poiseuille’s formula gives the volume of a liquid flowing out per second through a horizontal capillary tube of length l, radius r, under a pressure difference p applied across its ends.
Q=V/t=(πpr4)/8Ƞl.

7. Critical velocity of the liquid ___________
c) Decreased when density increases
d) Increases when density increases

Explanation:
vc=(Re Ƞ)/pD
Critically velocity decreases when density ρ increases or diameter D increases.

8. A steel ball is dropped in oil, then ___________
a) The ball attains constant velocity after sometime
b) The ball stops
c) The speed of ball will keep on increasing
d) The speed of the ball will decrease

Explanation: The ball attains constant velocity after falling through some distance in oil when the weight of ball gets balanced by upthrust and the upward viscous force.

9. An aeroplane gets its upward lift due to a phenomenon described by the ___________
a) Archimedes’ principle
b) Bernoulli’s principle
c) Buoyancy principle
d) Pascal law

Explanation: An aeroplane gets dynamic upward lift in accordance with Bernoulli’s principle.

10. The rate of flow of liquid through an orifice of a tank does not depend upon ___________
a) The size of the orifice
b) Density of liquid
c) The height of fluid column
d) Acceleration due to gravity

Explanation: The rate of flow of liquid through an orifice depends on the size of the orifice, atomising surface area, liquid characteristic. It does not depend on acceleration due to gravity.

11. The velocity of efflux of a liquid through an orifice in the bottom of the tank does not depend upon ___________
a) Size of orifice
b) Height of liquid
c) Acceleration due to gravity
d) Quantity

Explanation: Velocity of efflux, v=√2gh
Clearly, it does not depend on the size of the orifice.

12. Assertion: Smaller drops of liquid resist deforming forces better than the larger drops.
Reason: Excess pressure inside a drop is directly proportional to its surface area.
a) Both assertion and reason are true and the reason is the correct explanation of the assertion
b) Both assertion and reason are true but the reason is not the correct explanation of the assertion
c) Assertion is true but the reason is false
d) Assertion and reason is false

Explanation: The assertion is true but the reason is false. The excess pressure inside a liquid drop,
p=2σ/R
The excess pressure is large in a small drop due to which it can resist the deforming forces.

13. A body of mass 15kg is dropped into the water. If the apparent weight of the body is 107N, then the applied thrust will be ___________
a) 40 N
b) 80 N
c) 60 N
d) 100 N

Explanation: Apparent weight = Weight – Upthrust
Therefore, Upthrust = Weight – apparent weight
Upthrust = 15 × 9.8 – 107 = 147 – 107 = 40 N. 