This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Fluids Mechanical Properties Pressure – 1”.
1. When the area decreases _____
a) pressure increases
b) pressure decreases
c) pressure remains constant
d) the change in pressure cannot be determined
Explanation: Pressure (P) = Force (F)/Area (A)
From the above equation, we can see that the pressure is inversely proportional to area.
Hence, the pressure will increase when the area is decreased.
2. Pressure decreases when _____
a) only the force is increased but not the area
b) only the area is decreases but not the force
c) either area decreases or force increases
d) the force decreases and/or area increases
Explanation: Pressure (P) = Force (F)/Area (A)
From the above equation, we can infer that the pressure is inversely proportional to the area and directly proportional to the applied force.
Hence, the pressure will decrease when force is decreased and/or area is increased.
3. A force F is applied on a uniform rod of cross-section A and a force F’ is applied on a uniform rod of cross-section 3A. What is the relation between F and F’ if the pressure on both is the same?
a) F/F’ = 1/3
b) F/F’ = 3
c) F’/F = 1/3
d) F/F’ = 1/9
Explanation: Pressure on first rod (P) = F/A
Pressure on the second rod (P’) = F’/3A
P = P’
F/A = F’/3A
F/F’ = 1/3.
4. A force is applied on a cube of side 3m. Another force, double the magnitude of the previous force is applied on a cube of 1m. What is the ratio of pressure on the first cube (P) to the pressure on the second cube (P’)?
Explanation: P = F/32
P = F/9
P’ = 2F/12
P’ = 2F/1
P/P’ = (F/9)/(2F/1)
5. A force F is applied in a cross-sectional area as shown. The value of F is 20 N and the value of A is 2 m2. Find the pressure on the surface.
a) 20 Pa
b) 40 Pa
c) 5 Pa
d) 10 Pa
Explanation: Pressure (P) = Normal force(F) / Area (A)
The normal component of the given force is;
Fn = F * sin30°
P = 10/2
= 5 Pa.
6. 3 containers A, B, C are filled with water as shown in the figure. What is the relation between the pressures at 1, 2, 3? Assume that all jars are stationery.
Explanation: The pressure at a depth “d” in a liquid is;
P = D*g*d
P = Pressure
D = Density
g = Acceleration due to gravity
d = Depth
Here, d = Total height – h
From the equation, it is evident that the pressure does not depend on the cross-section of the jar when it is stationery. Hence, the pressure at 1, 2, 3 is the same.
7. Pascal’s Law is valid only for _____
Explanation: Pascal’s law is valid for water, gases and even other liquids. However, it is not applicable to any other form of matter. Hence, we can conclude that Pascal’s Law is valid only for fluids.
8. What is Pascal’s Law?
a) For every action, there is an equal and opposite reaction
b) Force is the time rate of change of momentum
c) For an ideal gas, the pressure is directly proportional to temperature and constant volume and mass
d) A pressure change at any point in the fluid is transmitted throughout the fluid such that the same change occurs everywhere
Explanation:For every action, there is an equal and opposite reaction – Newton’s Third Law
Force is the time rate of change of momentum – Newton’s Second Law
For an ideal gas, the pressure is directly proportional to temperature and constant volume and mass – Ideal Gas Law
A pressure change at any point in the fluid is transmitted throughout the fluid such that the same change occurs everywhere – Pascal’s Law.
9. From which of the following is the working of hydraulic machines based on?
a) Pascal’s Law
b) Newton’s Law of Cooling
c) Law of Gravitation
d) Ideal Gas Law
Explanation: Pascals Law states that a pressure change at any point in the fluid is transmitted throughout the fluid such that the same change occurs everywhere. This is employed in hydraulic machines by varying cross-sectional areas at required places.
10. The SI unit of pressure is _____
Explanation: The SI unit of pressure is “Pascal”. It is denoted by “Pa”.
1 Pa = 1 N/m2
It is named after the famous scientist Blaise Pascal.
11. Which of the following is used to measure pressure?
Explanation: A “barometer” is a scientific instrument used to measure air pressure. The barometer can also be used to measure the altitude of a region because pressure varies with altitude.
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