Question 1

What is the SI unit of force?

Accepted Answer

The SI unit of force is the Newton (N), named after Sir Isaac Newton. One Newton is defined as the force required to accelerate a mass of one kilogram at a rate of one metre per second squared (1 N = 1 kg⋅m/s²). This is derived from Newton's second law of motion (F = ma).

Question 2

Which physical quantity is measured in Hertz (Hz)?

Accepted Answer

Hertz (Hz) is the SI unit of frequency, named after German physicist Heinrich Hertz. One Hertz equals one cycle per second. Frequency measures how many times a periodic event occurs in one second, and is used for sound waves, electromagnetic waves, and oscillations.

Question 3

What is the SI unit of temperature?

Accepted Answer

The SI unit of temperature is the Kelvin (K), named after Scottish physicist William Thomson, Lord Kelvin. The Kelvin scale is an absolute temperature scale where 0 K represents absolute zero (the lowest possible temperature). Water freezes at 273.15 K and boils at 373.15 K at standard atmospheric pressure.

Question 4

Which scientist formulated the law of universal gravitation?

Accepted Answer

Sir Isaac Newton formulated the law of universal gravitation in 1687, published in his work 'Philosophiæ Naturalis Principia Mathematica' (Mathematical Principles of Natural Philosophy). This law states that every mass attracts every other mass with a force proportional to the product of their masses and inversely proportional to the square of the distance between them (F = G × m₁ × m₂ / r²).

Question 5

Which of the following is the SI unit of electric current?

Accepted Answer

The SI unit of electric current is the Ampere (A), named after French physicist André-Marie Ampère. It is defined as the flow of one coulomb of charge per second through a conductor.

Question 6

What is the phenomenon by which light bends when passing from one medium to another?

Accepted Answer

Refraction is the bending of light when it passes from one transparent medium to another with a different optical density. This occurs because light travels at different speeds in different media.

Question 7

A person standing on the ground experiences a normal force from the Earth. According to Newton's Third Law, what is the reaction force to this normal force?

Accepted Answer

According to Newton's Third Law of Motion, for every action, there is an equal and opposite reaction. The reaction force to the normal force exerted by Earth on a person is the force exerted by the person on the Earth (downward).

Question 8

Which of the following statements about friction is correct?

Accepted Answer

Friction is a force that opposes relative motion between two surfaces in contact. Static friction prevents motion from starting, while kinetic friction acts when surfaces are already sliding relative to each other.

Question 9

A ball is thrown vertically upward. At the highest point of its trajectory, what is the velocity of the ball?

Accepted Answer

At the highest point of a vertically thrown object's trajectory, the velocity becomes zero momentarily before the object begins to fall back down. This is because the upward velocity decreases due to gravitational acceleration until it reaches zero.

Question 10

When a person stands in front of a plane mirror, the image formed is virtual, erect, and of the same size as the object. Which of the following statements about this image is INCORRECT?

Accepted Answer

A plane mirror always forms a virtual image that is erect (upright) and the same size as the object. The image is formed at a distance behind the mirror equal to the distance of the object in front of the mirror. However, the image is laterally inverted (left-right reversed), not inverted top-to-bottom. The statement that the image is 'inverted' (meaning upside-down) is incorrect.

Question 11

In physics, the SI unit of force is the Newton (N). One Newton is equivalent to the force required to accelerate a mass of 1 kilogram at a rate of:

Accepted Answer

One Newton (N) is defined as the force needed to accelerate 1 kg of mass at 1 m/s². This is derived from Newton's second law: F = ma. When m = 1 kg and a = 1 m/s², then F = 1 N. This is a fundamental definition in classical mechanics and is universally standardized in the SI system.

Question 12

A person standing on the surface of Earth experiences gravitational acceleration of approximately 9.8 m/s². If the same person were standing on the surface of the Moon, the gravitational acceleration would be approximately:

Accepted Answer

The Moon's gravitational acceleration is approximately 1/6th that of Earth's. Since Earth's g ≈ 9.8 m/s², the Moon's g ≈ 9.8 ÷ 6 ≈ 1.6 m/s². This is due to the Moon's smaller mass (about 1/81 of Earth's mass) and smaller radius (about 1/4 of Earth's radius). The ratio of gravitational accelerations follows from Newton's law of universal gravitation: g = GM/r².

Question 13

When light travels from a denser medium (such as glass with refractive index n = 1.5) to a less dense medium (such as air with refractive index n = 1.0), the light bends away from the normal. This phenomenon is called:

Accepted Answer

This phenomenon is called refraction, specifically the bending of light as it crosses a boundary between two media with different optical densities. When light travels from a denser to a less dense medium, it bends away from the normal line (perpendicular to the surface). This is governed by Snell's Law: n₁ sin θ₁ = n₂ sin θ₂. The critical angle is the angle of incidence beyond which total internal reflection occurs instead of refraction.

Question 14

A simple pendulum oscillates with a time period T. If the length of the pendulum is increased to 4 times its original length, the new time period will be:

Accepted Answer

The time period of a simple pendulum is given by T = 2π√(L/g), where L is the length and g is gravitational acceleration. If length increases to 4L, then T_new = 2π√(4L/g) = 2π × 2√(L/g) = 2 × 2π√(L/g) = 2T. Therefore, the new time period is 2 times the original. This shows that time period is proportional to the square root of length, not directly proportional to length.

Question 15

A student observes that when a metal rod is heated at one end, the heat gradually spreads to the other end. Which of the following best explains this phenomenon and identifies the primary mode of heat transfer in solids?

Accepted Answer

In solids, heat transfer primarily occurs through conduction. When a metal rod is heated, the atoms at the heated end vibrate more vigorously. These vibrating atoms transfer kinetic energy to neighboring atoms through direct contact, causing the heat to propagate along the rod. This is the dominant mechanism in solids because the atoms are tightly packed and cannot move freely (unlike in fluids where convection occurs). The rate of conduction depends on the thermal conductivity of the material—metals have high thermal conductivity, which is why metal rods conduct heat efficiently.

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