Physics MCQs
Topic Notes: Physics
MCQs and preparation resources for competitive exams, covering important concepts, past papers, and detailed explanations.
Plato
- Biography: Ancient Greek philosopher (427–347 BCE), student of Socrates and teacher of Aristotle, founder of the Academy in Athens.
- Important Ideas:
- Theory of Forms
- Philosopher-King
- Ideal State
1
The Mach number is a dimensionless quantity used to describe an object's speed relative to which physical standard?
Answer:
The speed of sound
The Mach number is defined as the ratio of the speed of an object moving through a fluid to the local speed of sound in that same medium. It is a critical parameter in aerodynamics, as it helps characterize the flow regime, such as subsonic, transonic, or supersonic, based on the speed of sound.
2
Calculate the force exerted on a stationary wall by a water jet striking it normally, given a flow rate of 0.0001 m³/s and a velocity of 10 m/s.
Answer:
1 N
The force exerted by a fluid jet on a surface is determined by the rate of change of momentum, expressed as F = ρ * Q * v, where ρ is the density of water (1000 kg/m³), Q is the volumetric flow rate (0.0001 m³/s), and v is the velocity (10 m/s). Calculating this: 1000 * 0.0001 * 10 = 1 Newton. This force represents the impact of the water mass against the wall.
3
Which fundamental conservation law serves as the basis for deriving the equation of continuity?
Answer:
Mass
The equation of continuity is derived from the principle of conservation of mass. It asserts that for an incompressible fluid flowing through a pipe, the mass of fluid entering the pipe must equal the mass of fluid exiting the pipe per unit time, resulting in the product of cross-sectional area and velocity being constant.
4
In the context of streamline fluid flow, which of the following statements is correct regarding the velocity of fluid particles?
Answer:
the velocity of all fluid particles crossing a given position is constant
In steady or streamline flow, the velocity of fluid particles at any specific point in space remains constant over time. While individual particles may change velocity as they move along different streamlines, the flow pattern at any fixed location does not change, ensuring consistent velocity for any particle passing through that point.
5
In the continuity equation A₁V₁ = A₂V₂ = constant, what physical quantity does the constant represent?
Answer:
Flow rate
The product of the cross-sectional area (A) and the velocity (V) of the fluid at any point in a pipe represents the volumetric flow rate (Q). Since the fluid is assumed to be incompressible, the volume of fluid passing through any cross-section per unit time must remain constant, which is the core premise of the continuity equation.
6
The equation of continuity in fluid dynamics is derived from which fundamental conservation law?
Answer:
Mass
The equation of continuity is a mathematical expression of the law of conservation of mass. It states that for a steady flow of an incompressible fluid through a pipe of varying cross-sectional area, the mass of fluid entering the pipe must equal the mass of fluid exiting the pipe per unit time, ensuring no accumulation of mass within the system.
7
The Mach number is a dimensionless quantity primarily used to describe the speed of which of the following?
Answer:
aircraft
The Mach number is defined as the ratio of the speed of an object, such as an aircraft, to the speed of sound in the surrounding medium. It is a critical parameter in aerodynamics for characterizing the flow regime, such as subsonic, transonic, or supersonic flight.
8
Calculate the force exerted on a wall by a water jet striking it normally at 10 m/s with a discharge rate of 0.0001 m³/s.
Answer:
1 Newton
The force exerted by a jet is given by F = mass flow rate × velocity. Mass flow rate = density × discharge = 1000 kg/m³ × 0.0001 m³/s = 0.1 kg/s. Force = 0.1 kg/s × 10 m/s = 1 Newton.
9
When measuring the speed of an object using the Mach number, what is the reference speed used for comparison?
Answer:
The speed of sound
The Mach number is a dimensionless quantity in fluid dynamics representing the ratio of the speed of an object to the speed of sound in the surrounding medium. It is used to characterize the flow regime, such as subsonic, transonic, supersonic, or hypersonic, based on how the object's speed compares to the local speed of sound.
10
In the equation of continuity A1V1 = A2V2, what physical quantity does the constant represent?
Answer:
Flow rate
The constant in the equation of continuity represents the volumetric flow rate, often denoted as Q. It is defined as the volume of fluid passing through a given cross-section per unit of time. Because the fluid is incompressible, this rate remains constant throughout the entire flow path.