Q40. Which statement about work done by gravity is incorrect?
[UPSC NDA-II GAT — 14 Sep 2025]
(A) It is independent of the path
(B) It depends on vertical separation of endpoints
(C) It depends on the route followed
(D) It is zero for horizontal displacement
Answer: (C) It depends on the route followed
Explanation: Gravity is a conservative force. In a nearly uniform field its work is mg times the downward change in height, irrespective of the route. A purely horizontal displacement produces zero gravitational work; path dependence is therefore the incorrect claim.
Q39. Two unequal-mass bodies are released together from a tower. Ignoring drag, which quantity is equal for them at each instant?
[UPSC NDA-I GAT — 13 Apr 2025]
(A) Momentum
(B) Acceleration
(C) Potential energy
(D) Kinetic energy
Answer: (B) Acceleration
Explanation: Both bodies are subject to the same local gravitational acceleration g. Momentum and energies contain their differing masses and generally differ. When released at the same time, each gains the same speed, even though their masses are unequal.
Q38. How does g at Earth’s poles compare with g at the equator?
[RRB Technician Grade III — 28 Dec 2024, Shift 3]
(A) It is negative at the equator
(B) It is greater at the equator
(C) It is equal at both
(D) It is greater at the poles
Answer: (D) It is greater at the poles
Explanation: Earth’s flattened shape places the poles nearer the centre. Rotation also reduces effective gravity most at the equator. These effects together make surface gravitational acceleration slightly higher at the poles than at the equator.
Q37. A body is thrown upward. How is the direction of gravity related to its motion during ascent?
[RRB Technician Grade III — 28 Dec 2024, Shift 2]
(A) In the same direction
(B) Gravity is zero
(C) Opposite to its motion
(D) Gravity always follows its motion
Answer: (C) Opposite to its motion
Explanation: Although the body initially travels upward, gravity always pulls toward Earth’s centre. Its downward force reduces upward velocity. The body momentarily stops at the top, and then begins accelerating downward under the same gravitational force.
Q36. What force accelerates an object that falls toward Earth?
[RRB Technician Grade III — 28 Dec 2024, Shift 1]
(A) An outward repulsive force
(B) Earth’s gravitational attraction
(C) Nuclear force
(D) Electromagnetic force
Answer: (B) Earth’s gravitational attraction
Explanation: A freely falling object is pulled earthward by gravitational force. Newton’s second law converts that force into acceleration. Near Earth’s surface, the acceleration is approximately 9.8 m/s² if resistive forces such as air drag are negligible.
Q35. Compared with Earth, what happens to the weight of a body on the Moon?
[RRB Technician Grade III — 27 Dec 2024, Shift 3]
(A) It depends on body density alone
(B) It becomes smaller
(C) It becomes greater
(D) It remains equal
Answer: (B) It becomes smaller
Explanation: The Moon’s surface gravitational acceleration is about one-sixth of Earth’s. Since weight equals mass multiplied by local g, the same body weighs much less on the Moon. Its mass, however, remains unchanged during the transfer.
Q34. How does the near-surface gravitational acceleration of an object depend on its own mass m?
[RRB Technician Grade III — 26 Dec 2024, Shift 2]
(A) It is independent of m
(B) It varies as m²
(C) It varies inversely as m
(D) It is directly proportional to m
Answer: (A) It is independent of m
Explanation: Equating gravitational force GMm/R² to inertial force ma cancels the falling mass m and gives a = GM/R². Thus, in the absence of air drag, objects of different masses fall with the same local acceleration.
Q33. At what stage of a body’s free fall from height h is kinetic energy the largest?
[RRB Technician Grade III — 24 Dec 2024, Shift 2]
(A) After one-quarter of the distance
(B) Immediately after release
(C) After half the distance
(D) Immediately before impact
Answer: (D) Immediately before impact
Explanation: A falling body accelerates downward and gains speed throughout its descent. Kinetic energy depends on the square of speed, so it grows as the body approaches the ground. Without air resistance, it is greatest immediately before impact.
Q32. Which listed equation correctly relates initial and final velocity in uniform acceleration?
A: s = ut + 2at²;
B: v = u + ½at;
C: v − u = at.
[RRB Technician Grade III — 23 Dec 2024, Shift 2]
(A) Both B and C
(B) Only C
(C) Both A and B
(D) Only A
Answer: (B) Only C
Explanation: Acceleration is the rate of change in velocity. For constant a, a = (v − u)/t, so v − u = at. The other given relations use incorrect factors of acceleration and do not match standard kinematic equations.
Q31. An astronaut in the orbiting space station feels weightless. What quantity is zero?
[UPSC NDA-II GAT — 01 Sep 2024]
(A) Astronaut’s acceleration
(B) Normal reaction from the station floor
(C) Gravitational attraction of Earth
(D) Earth’s centripetal acceleration
Answer: (B) Normal reaction from the station floor
Explanation: Astronaut and station are both in continuous orbital free fall, accelerating under gravity together. Thus the floor exerts essentially no supporting normal force on the astronaut. Earth’s gravitational pull and the orbital centripetal acceleration are not zero.
