NDA General Knowledge (Physics) - Work, Power & Energy, Gravitation Practice Test 50 MCQs

NDA General Knowledge (Physics) - Work, Power & Energy, Gravitation Practice Test

Targeted 50 MCQ Practice Module for NDA Paper II (Part B: General Knowledge - Physics) covering: Work, Power & Energy, and Gravitation.

Select your answers and click Submit Assessment Answers at the bottom to calculate your total score and review explanations.

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SECTION I: Work - Basic Concepts [Questions 1 to 10]

1. Work done by a force is defined as the product of force and:

Time taken Displacement in the direction of force Velocity of the object Acceleration produced

Explanation: Work W = F·d·cosθ, i.e., force multiplied by the displacement component in the direction of the force.

2. The SI unit of work is the:

Newton Watt Joule Erg

Explanation: Work is measured in Joules (J), where 1 Joule = 1 Newton × 1 metre.

3. If a force is applied on a body but the body does not move at all, the work done is:

Maximum Negative Equal to the force applied Zero

Explanation: Since W = F·d·cosθ, if displacement d = 0, the work done is zero regardless of the force applied.

4. When the angle between the applied force and the displacement is 90°, the work done is:

Zero Maximum Negative Equal to F × d

Explanation: cos 90° = 0, so W = F·d·cos90° = 0. This is why the work done by centripetal force in circular motion is zero.

5. Work done is said to be negative when:

Force and displacement are in the same direction There is no displacement Force and displacement are in opposite directions The angle between force and displacement is 0°

Explanation: When θ is between 90° and 180° (e.g., friction opposing motion), cosθ is negative, making the work done negative.

6. 1 Joule is equivalent to how many ergs?

10^5 erg 10^7 erg 10^3 erg 10^9 erg

Explanation: 1 Joule = 1 kg·m²/s² = 10^7 g·cm²/s² = 10^7 erg (the CGS unit of work/energy).

7. The dimensional formula of work is:

[ML²T⁻²] [MLT⁻²] [ML²T⁻³] [MLT⁻¹]

Explanation: Work = Force × Distance = [MLT⁻²] × [L] = [ML²T⁻²], the same dimensional formula as energy.

8. Work is a:

Vector quantity Complex quantity Dimensionless quantity Scalar quantity

Explanation: Even though force and displacement are vectors, work is the dot product of the two and hence is a scalar quantity.

9. A coolie carrying a load on his head and walking on a level platform does no work in the physics sense because:

He is moving too slowly The load has no mass The force (vertical) is perpendicular to the displacement (horizontal) Friction cancels all the work done

Explanation: The applied vertical support force makes a 90° angle with the horizontal displacement, so cosθ = 0 and the work done is zero.

10. Work done by gravity on a freely falling body of mass m through a height h is:

Zero +mgh -mgh mgh²

Explanation: Since gravity and displacement act in the same downward direction during a fall, the work done by gravity is positive and equals mgh.

SECTION II: Power [Questions 11 to 20]

11. Power is defined as the rate of doing:

Work Force Displacement Momentum

Explanation: Power P = Work done / Time taken = W/t.

12. The SI unit of power is the:

Joule Newton Watt Pascal

Explanation: Power is measured in Watts, where 1 Watt = 1 Joule per second.

13. 1 horsepower (HP) is approximately equal to:

550 W 746 W 1000 W 100 W

Explanation: 1 Horsepower = 746 Watts, a unit historically used to compare engine output to the power of a horse.

14. Instantaneous power delivered by a force F acting on a body moving with velocity v is given by:

P = F + v P = F/v P = F × t P = F · v (dot product)

Explanation: Since P = dW/dt and dW = F·dx, instantaneous power is the dot product of force and velocity, P = F·v·cosθ.

15. The dimensional formula of power is:

[ML²T⁻³] [ML²T⁻²] [MLT⁻²] [ML⁻¹T⁻²]

Explanation: Power = Work/Time = [ML²T⁻²]/[T] = [ML²T⁻³].

16. If two machines perform the same amount of work, but Machine A takes half the time of Machine B, then:

Machine B has more power Both have equal power Machine A has twice the power of Machine B Power cannot be compared

Explanation: Since P = W/t and Machine A takes half the time for the same work, its power output is double that of Machine B.

17. A "kilowatt-hour" (kWh), commonly used on electricity bills, is a unit of:

Power Energy (Work) Force Current

Explanation: Despite the name including "watt", a kWh measures energy consumed (power × time), equal to 3.6 × 10⁶ Joules.

18. A man pushes hard against a rigid wall and gets exhausted, but in the strict physics sense, the work done on the wall is:

Very large Equal to his muscular energy spent Negative Zero

Explanation: Since the wall does not move, displacement is zero, so the mechanical work done on the wall is zero even though internal biological energy is expended.

19. Average power over a time interval is calculated as:

Total work done ÷ Total time taken Total work done × Total time taken Force × Time Change in velocity ÷ Time

Explanation: Average power = ΔW/Δt, the total work performed divided by the total time taken to perform it.

20. The power rating (in Watts) marked on an electrical appliance such as a bulb indicates:

The total energy it will consume in its lifetime Its voltage rating only The rate at which it consumes electrical energy Its resistance value

Explanation: The wattage rating tells us the rate of energy consumption (or conversion) of the appliance per unit time.

SECTION III: Work-Energy Theorem & Conservation of Energy [Questions 21 to 30]

21. The kinetic energy of a body of mass m moving with velocity v is given by:

mv ½mv² mv² 2mv²

Explanation: Kinetic Energy (KE) is defined as ½mv², the energy possessed by a body due to its motion.

22. According to the Work-Energy Theorem, the net work done on a body equals:

The change in its kinetic energy The change in its potential energy Its total mechanical energy Its momentum

Explanation: The Work-Energy Theorem states that W_net = ΔKE = KE_final − KE_initial.

23. The Law of Conservation of Energy states that energy:

Can be created but not destroyed Can be destroyed but not created Increases continuously in an isolated system Can neither be created nor destroyed, only transformed from one form to another

Explanation: The total energy of an isolated system remains constant; energy merely changes form (e.g., PE to KE).

24. The total mechanical energy (KE + PE) of a body remains conserved when:

Only friction acts on it Air resistance acts on it Only conservative forces (like gravity) act on it The body is at rest

Explanation: Mechanical energy is conserved only in the absence of non-conservative (dissipative) forces such as friction or air resistance.

25. The potential energy stored in a compressed or stretched spring (spring constant k, extension x) is:

kx ½kx² kx² 2kx

Explanation: Elastic Potential Energy stored in a spring is given by ½kx², where k is the spring (force) constant and x is deformation.

26. In a perfectly elastic collision between two bodies:

Both kinetic energy and momentum are conserved Only momentum is conserved, KE is lost Only KE is conserved, momentum is lost Neither KE nor momentum is conserved

Explanation: An elastic collision is one in which both the total kinetic energy and the total momentum of the system remain unchanged.

27. In a perfectly inelastic collision, the colliding bodies:

Bounce back with the same speed Conserve kinetic energy fully Lose momentum Stick together and move with a common velocity, with kinetic energy loss

Explanation: In a perfectly inelastic collision, momentum is conserved but bodies coalesce and move together, with some kinetic energy converted to heat/sound/deformation.

28. A ball thrown vertically upward reaches its maximum height when:

Its kinetic energy is maximum Its velocity (and kinetic energy) becomes zero Its potential energy is zero Acceleration becomes zero

Explanation: At the highest point of a vertical throw, the velocity momentarily becomes zero, so kinetic energy is zero and all energy is potential.

29. Which of the following is an example of the conversion of potential energy into kinetic energy?

A stretched bow held steady A charged battery at rest Water falling from a height in a dam A book resting on a table

Explanation: As water falls from a height, its gravitational potential energy is progressively converted into kinetic energy, which is later used to generate hydroelectric power.

30. Which law of thermodynamics is essentially another statement of the law of conservation of energy?

First Law of Thermodynamics Second Law of Thermodynamics Third Law of Thermodynamics Zeroth Law of Thermodynamics

Explanation: The First Law of Thermodynamics states that energy can neither be created nor destroyed, only converted from one form to another — the same principle as conservation of energy.

SECTION IV: Gravitation - Newton's Law & Variation of 'g' [Questions 31 to 40]

31. According to Newton's Law of Gravitation, the gravitational force between two masses is:

Directly proportional to the distance between them Independent of their masses Directly proportional to the product of their masses and inversely proportional to the square of the distance between them Inversely proportional to the product of their masses

Explanation: Newton's Law of Gravitation: F = G·m1·m2/r², where G is the universal gravitational constant.

32. The approximate value of the universal gravitational constant (G) is:

9.8 N m²/kg² 6.674 × 10⁻¹¹ N m²/kg² 3 × 10⁸ N m²/kg² 1.6 × 10⁻¹⁹ N m²/kg²

Explanation: The universal gravitational constant G has an approximate value of 6.674 × 10⁻¹¹ N m²/kg².

33. Who first experimentally measured the value of the gravitational constant (G)?

Henry Cavendish Johannes Kepler Galileo Galilei Albert Einstein

Explanation: Henry Cavendish first measured the value of G experimentally in 1798 using a torsion balance.

34. The approximate standard value of acceleration due to gravity (g) at the Earth's surface (sea level) is:

6.67 m/s² 3.8 m/s² 11.2 m/s² 9.8 m/s²

Explanation: The standard value of acceleration due to gravity at the Earth's surface is approximately 9.8 m/s².

35. As altitude above the Earth's surface increases, the value of acceleration due to gravity (g):

Increases Decreases Remains constant First increases, then decreases

Explanation: Since g ∝ 1/r², as height above Earth's surface increases, the distance from Earth's centre increases and g decreases.

36. As one goes deeper below the Earth's surface (towards the centre), the value of 'g':

Increases and becomes maximum at the centre Remains constant throughout Decreases and becomes zero at the centre Becomes negative

Explanation: Below the surface, only the mass enclosed within that radius contributes to g, so g decreases linearly with depth and becomes zero at the Earth's centre.

37. The value of 'g' is greatest at the:

Poles Equator Tropic of Cancer Same everywhere on Earth

Explanation: Due to Earth's oblate shape (flattened at poles) and its rotation, the value of g is maximum at the poles and minimum at the equator.

38. The weight of a body is given by W = mg. If a body is taken from Earth to the Moon, its:

Mass changes but weight remains the same Both mass and weight remain the same Mass increases and weight decreases Mass remains the same but weight decreases (since g on Moon is less)

Explanation: Mass is an intrinsic property that does not change with location, but weight (mg) decreases on the Moon since the Moon's gravitational acceleration is about 1/6th that of Earth.

39. In the absence of air resistance, a heavy stone and a light feather dropped simultaneously from the same height will:

The stone will reach the ground first Both will reach the ground at the same time The feather will reach the ground first Neither will fall

Explanation: Acceleration due to gravity is independent of the mass of the falling object; in a vacuum, all bodies fall with the same acceleration 'g'.

40. The nature of the gravitational force between any two masses in the universe is always:

Repulsive Sometimes attractive, sometimes repulsive Attractive Neutral (neither attractive nor repulsive)

Explanation: Unlike electric forces, gravitational force is always attractive in nature and follows an inverse-square law.

SECTION V: Gravitational PE, Escape Velocity, Satellites & Kepler's Laws [Questions 41 to 50]

41. The gravitational potential energy of a body of mass m at a distance r from the centre of the Earth (mass M) is given by:

−GMm/r +GMm/r GMm/r² mgr

Explanation: Gravitational PE is taken as negative (with zero reference at infinity) and is given by U = −GMm/r, becoming less negative as r increases.

42. The escape velocity of a body from a planet of mass M and radius R is given by the formula:

v = GM/R v = √(2GM/R) v = √(GM/R) v = 2GM/R²

Explanation: Escape velocity is derived by equating kinetic energy to the magnitude of gravitational PE: ½mv² = GMm/R, giving v = √(2GM/R).

43. The approximate escape velocity from the surface of the Earth is:

7.9 km/s 9.8 km/s 2.4 km/s 11.2 km/s

Explanation: The escape velocity from Earth's surface is approximately 11.2 km/s, the minimum speed needed to escape Earth's gravitational pull permanently.

44. The orbital velocity required for a satellite to revolve in a circular orbit close to the Earth's surface (first cosmic velocity) is approximately:

7.9 km/s 11.2 km/s 3.6 km/s 16.7 km/s

Explanation: The orbital (first cosmic) velocity near the Earth's surface is about 7.9 km/s, which is escape velocity divided by √2.

45. A geostationary satellite has an orbital time period of:

12 hours 90 minutes 24 hours 365 days

Explanation: A geostationary satellite has a period of 24 hours, matching Earth's rotation, so it appears stationary relative to a point on Earth's surface.

46. According to Kepler's First Law of Planetary Motion, planets move around the Sun in:

Perfect circles with the Sun at the centre Elliptical orbits with the Sun at one of the foci Parabolic paths Straight lines

Explanation: Kepler's First Law (Law of Orbits) states that every planet moves in an elliptical orbit with the Sun located at one focus of the ellipse.

47. Kepler's Second Law (Law of Areas) implies that a planet moves:

At constant speed throughout its orbit Slowest when nearest to the Sun In a straight line towards the Sun Faster when nearer to the Sun (perihelion) and slower when farther (aphelion)

Explanation: Kepler's Second Law states that the radius vector sweeps out equal areas in equal times, meaning the planet moves faster at perihelion and slower at aphelion.

48. Kepler's Third Law (Law of Periods) states that the square of the time period (T) of a planet's revolution is proportional to:

The cube of the semi-major axis (mean orbital radius), i.e., T² ∝ r³ The square of the orbital radius, i.e., T² ∝ r² The orbital radius directly, i.e., T² ∝ r The mass of the planet

Explanation: Kepler's Third Law states T² ∝ r³, relating the square of the orbital period to the cube of the semi-major axis of the orbit.

49. The escape velocity of a body from a given planet is independent of:

The mass of the planet The radius of the planet The mass of the escaping body The gravitational constant G

Explanation: Since v = √(2GM/R), escape velocity depends only on the mass and radius of the planet, not on the mass of the object attempting to escape.

50. Astronauts inside an orbiting satellite experience "weightlessness" mainly because:

There is no gravity at all in orbit The satellite and astronauts are in a continuous state of free fall around the Earth Their mass becomes zero in space The satellite is stationary in space

Explanation: Gravity still acts on the satellite and astronauts, providing the centripetal force for orbit; since both are in continuous free fall together, the apparent (normal reaction) weight becomes zero.

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