Physics: Mechanics: UPSC Previous Year Questions (Science and Technology)

Explanation

Option 1 is incorrect: While radial tyres improve handling and durability, they primarily reduce rolling resistance, which can have a minor impact on fuel efficiency. However, their primary benefit is not directly linked to significant fuel savings.

Option 2 is correct: A streamlined body reduces aerodynamic drag, allowing the car to move more efficiently through the air. This directly improves fuel efficiency, especially at higher speeds. An example of a car with a streamlined body is the Tesla Model S. Its sleek, aerodynamic design minimizes air resistance, improving both fuel efficiency (or energy efficiency in the case of electric cars) and performance.

Option 3 is correct: Multipoint Fuel Injection ensures that the right amount of fuel is injected into each cylinder, improving combustion efficiency and reducing fuel consumption.

Option 4 is incorrect: While a catalytic converter reduces harmful emissions, it does not directly affect fuel efficiency. Its primary function is to convert toxic gases like carbon monoxide into less harmful substances. Direction: The following item consists of two statements, one labeled as the Assertion (A) and the other as Reason (R). You have to answer these items using the code given below.

Explanation

According to Newton’s first law of motion, " A body at rest will remain at rest, and a body in motion will continue in uniform motion in a straight line unless acted upon by an external force". According to Newton’s second law of motion, "The rate of change of momentum of a body is directly proportional to the applied force and occurs in the direction of the force". Assertion (A) is true: When the man whistles, he expels air from his lungs. This expelled air has mass and velocity, creating momentum in the forward direction and thus creating reaction force which pushes the man backward on the frictionless surface. This is based on Newton’s second law of motion. Reason (R) is true: The statement that ‘ if no external force acts on a system, its momentum cannot change’ is clearly stating Newton>s first law of motion which is clearly not explaining the Assertion (A). Thus, Reason (R) merely states Newton’s First Law of Motion and doen’s explain the Assertion (A) which is based on Newton’s Second Law of Motion.