Physics: Mechanics: UPSC Previous Year Questions (Science and Technology)
14 previous year UPSC Prelims questions on mechanics appear here, from 1997 to 2004. UPSC asks conceptual questions on weight and altitude, buoyancy and floating, the pendulum, motion in a circle and uniform motion. The explanations reason from the physical principle, so no formula-heavy working is needed to follow them.
Explanations state facts as of the year each question was asked; words like “recently” refer to that year.
Showing 11–14 of 14 questions
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UPSC 1999Science and Technology · Physics: Mechanics
Q11. For which one of the following is capillarity not the reason?
Explanation
Capillarity, also known as capillary action, is the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. Capillarity is crucial in various natural and artificial processes, where the balance of forces drives the liquid into confined spaces.
Option (a) is correct: The tiny pores in the blotting paper act as capillaries and draw the ink through them.
Option (b) is incorrect: This is primarily due to hydrostatic pressure and not capillary action. Water moves through soil and rock layers due to pressure gradients rather than the effects of surface tension.
Option (c) is correct: This is due to capillarity. The fine fibers in the cloth act as capillaries, drawing water into them.
Option (d) is correct: Capillary action, along with transpiration pull and root pressure, helps move water through the tiny xylem vessels in plants.
UPSC 1997Science and Technology · Physics: Mechanics
Q12. The tendency of a liquid drop to contract and occupy minimum area is due to:
Explanation
Surface tension is the force that acts on the surface of a liquid, causing it to contract and minimize its surface area. This effect occurs because molecules at the surface of the liquid experience a net inward force due to the attractive forces between the molecules. As a result, the liquid tends to form shapes that have the least surface area, such as spherical droplets. This tendency to minimize surface area is why liquid droplets form spherical shapes in free space, as a sphere has the smallest surface area for a given volume.
UPSC 1997Science and Technology · Physics: Mechanics
Q13. Which one of the following is a vector quantity?
Explanation
A vector quantity is a physical quantity that has both magnitude and direction. In addition to how much of a quantity there is, you also need to know the direction in which it acts. Some examples of vector quantities include force, velocity, acceleration and displacement. Momentum is a vector quantity because it has both magnitude and direction (it depends on the direction of motion and the velocity of the object).
UPSC 1997Science and Technology · Physics: Mechanics
Q14. The working principle of a washing machine is:
Explanation
Option (a) is correct: The working principle of a washing machine is Centrifugation. It is a process used to separate substances of different densities by spinning them at high speed. In a washing machine, the centrifugal force generated during the spin cycle helps remove water from the clothes along with dirt and stain.
Option (b), (c) and (d) are incorrect:
Dialysis is a process used to remove waste products and excess fluids from the blood in patients with kidney failure. It involves the diffusion of solutes across a semipermeable membrane. Reverse osmosis is a water purification process that uses a semipermeable membrane to remove ions, molecules and larger particles from water. It is commonly used in desalination and water filtration systems. Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. While diffusion plays a role in processes like the mixing of detergents in water but it is not the main working principle of a washing machine.
Answer key for these questions
Q
UPSC year
Correct answer
11
1999
(b) Rising of underground water
12
1997
(a) surface tension
13
1997
(a) Momentum
14
1997
(a) Centrifugation
What UPSC has tested in Physics: Mechanics
The weight of a body decreases with the increase of altitude on the earth because gravity weakens with distance from the centre.
A weightless balloon filled with water has zero weight in water, because the weight is balanced by the buoyant force.
An iron ball floats on mercury but sinks in water because mercury is denser than iron.
A man on a completely frictionless surface can propel himself by throwing an object.
Frequently asked questions
How many previous year UPSC questions are there on Physics: Mechanics?
This page covers 14 previous year UPSC Prelims GS Paper-I questions on Physics: Mechanics (Science and Technology), asked from 1997 to 2004. Each has the correct answer and an explanation.
Why does the weight of a body decrease with altitude?
Because the pull of gravity falls as the distance from the Earth’s centre increases. Mass stays the same, but the weight, which is the force of gravity on the body, becomes slightly smaller at higher altitude.
Why does an iron ball float on mercury but sink in water?
An object floats when its density is less than that of the liquid. Iron is denser than water, so it sinks there, but mercury is denser than iron, so the iron ball floats on it.
