Fluid Mechanics Questions and Answers – Fluid Pressure at a Point and Pascal’s Law

This set of Fluid Mechanics Questions and Answers for Experienced people focuses on “Fluid Pressure at a Point & Pascal’s Law”.

1. A Hydraulic press has a ram of 30 cm diameter and a plunger of of 2 cm diameter. It is used for lifting a weight of 35 kN. Find the force required at the plunger.
a) 233.3 kN
b) 311.1 kN
c) 466.6 kN
d) 155.5 kN
View Answer

Answer: d
Explanation: F/a=W/A
F=(35000*3.142*.02*.02)/(3.142*0.3*0.3)
=155.5 kN.

2. The pressure at a point in the fluid is 4.9 N/cm2. Find height when the fluid under consideration is in oil of specific gravity of 0.85.
a) 5.83 m
b) 11.66 m
c) 17.49 m
d) 8.74 m
View Answer

Answer: a
Explanation: Height=p/ρg
=48620/850*9.81
=5.83 m.

3. An open tank contains water upto a depth of 350 cm and above it an oil of specific gravity 0.65 for a depth of 2.5 m. Find the pressure intensity at the extreme bottom of the tank.
a) 5.027 N/cm2
b) 10.05 N/cm2
c) 2.51 N/cm2
d) None of the mentioned
View Answer

Answer: a
Explanation: p= (specific gravity of water* height of water + specific gravity of oil* height of oil) * 9.81
= 5.027 N/cm2.
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4. The diameters of a small piston and a large piston of a hydraulic jack are 45 mm and 100 mm respectively.Force of 0.09 kN applied on smaller in size piston. Find load lifted by piston if smaller in size piston is 40 cm above the large piston. The density of fluid is 850 kg/m3
a) 60 N/cm2
b) 12 N/cm2
c) 30 N/cm2
d) None of the mentioned
View Answer

Answer: a
Explanation: Pressure at bottom of tank =ρgh + F/a
=850*9.81*0.4 + 90/3.142*0.045*0.045
=60 N/cm2.

5. If fluid is at rest in a container of a narrow mouth at a certain column height and same fluid is at rest at same column height in a container having broad mouth, will the pressure be different at certain depth from fluid surface.
a) Pressure will be same for both.
b) Pressure will be more for narrower mouth
c) Pressure will be less for narrower mouth
d) None of the mentioned
View Answer

Answer: a
Explanation: As per hydrostatic law, the pressure depends only on the height of water column and not its shape.
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6. We can draw Mohr’s circle for a fluid at rest.
a) True
b) false
View Answer

Answer: b
Explanation: Mohr’s circle is used to denote shear stress distribution. For fluid at rest, there is no shear stress. Hence, we cannot draw Mohr’s circle for fluid at rest.

7. Pressure intensity or force due to pressure gradient for fluid at rest is considered as which kind of force?
a) Surface force
b) Body force
c) Force due to motion
d) None of the mentioned
View Answer

Answer: a
Explanation: Pressure force is surface force.
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8. Calculate the hydrostatic pressure for water moving with constant velocity at a depth of 5 m from the surface.
a) 49 kN/m2
b) 98 kN/m2
c) since fluid is in motion, we cannot analyse
d) None of the mentioned
View Answer

Answer: a
Explanation: If fluid is moving with uniform velocity we treat it analytically same as if fluid is at rest
p= ρgh.

9. Pressure distribution for fluid at rest takes into consideration pressure due to viscous force.
a) True
b) False
View Answer

Answer: b
Explanation: Viscous force term in pressure expression for fluid at rest is absent as their is no motion of liquid.
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10. Barometer uses the principle of fluid at rest or pressure gradient for its pressure calculation.
a) True
b) False
View Answer

Answer: a
Explanation: Principle of Barometer is Hydrostatic law.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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