Q30. When a stone is thrown upward, which energy conversion predominantly occurs during the ascent?
[SSC MTS — 12 Sep 2023, Shift 3]
(A) Kinetic energy into unspecified mechanical energy
(B) Potential energy into gravitational energy
(C) Mechanical energy into kinetic energy
(D) Kinetic energy into gravitational potential energy
Answer: (D) Kinetic energy into gravitational potential energy
Explanation: As the stone rises against gravity, its speed decreases and so does its kinetic energy. Its height and gravitational potential energy increase. Under ideal conditions, total mechanical energy remains constant while kinetic energy converts into potential energy.
Q29. As a body falls from a height, which of these quantities remains uniform?
[UPSC CDS-II General Knowledge — 04 Sep 2022]
(A) Acceleration
(B) Momentum
(C) Kinetic energy
(D) Potential energy
Answer: (A) Acceleration
Explanation: Assuming air resistance can be ignored and the fall is close to Earth’s surface, gravitational acceleration g is approximately constant. Momentum and kinetic energy increase as speed rises, while potential energy decreases with height.
Q28. Which dimensionless number is especially associated with gravitational forces in fluid motion?
[MPPSC Assistant Engineer Mechanical — 03 Jul 2022]
(A) Froude number
(B) Mach number
(C) Weber number
(D) Euler number
Answer: (A) Froude number
Explanation: The Froude number compares inertial effects with gravity in flowing fluids: Fr = V/√(gL), where L is a characteristic length. It is relevant to gravity-driven free-surface motion such as open-channel flow, waves and spillways.
Q27. Lifting an object, an army parade and a vertically falling object exemplify which type of motion?
[SSC CHSL 2021 Paper — 01 Jun 2022, Shift 2]
(A) Rectilinear motion
(B) Periodic motion
(C) Rotational motion
(D) Oscillatory motion
Answer: (A) Rectilinear motion
Explanation: These examples involve motion along a straight line, whether vertical or horizontal, and thus are rectilinear. A falling object may have changing speed, but its trajectory can still be straight. Uniform speed is not essential for rectilinear motion.
Q26. Which is NOT an example of projectile motion?
[SSC JE Mechanical — 22 Mar 2021, Evening]
(A) A stone thrown into the air
(B) A stone launched horizontally from a roof
(C) A car moving straight on a road
(D) A bullet fired from a gun
Answer: (C) A car moving straight on a road
Explanation: A projectile moves after launch primarily under gravity, following a curved trajectory in the ideal model. A car driving on a road is propelled and constrained by contact forces, so its straight-line motion is not projectile motion.
Q25. A 60 kg man has an apparent mass reading of 54 kg in a downward-accelerating lift. What is the lift acceleration?
[UPPSC Assistant Engineer Mechanical — 13 Dec 2020]
(A) 1.26 m/s²
(B) 1.98 m/s²
(C) 0.98 m/s²
(D) 1.76 m/s²
Answer: (C) 0.98 m/s²
Explanation: The scale force is N = m(g − a). A reading equivalent to 54 kg gives 54g = 60(g − a). Therefore a = (1 − 54/60)g = 0.1g, approximately 0.98 m/s² downward.
Q24. What is the force called by which Earth draws objects toward itself?
[SSC CHSL — 12 Oct 2020, Shift 3]
(A) Air pressure
(B) Thrust
(C) Gravity
(D) Resistance
Answer: (C) Gravity
Explanation: Gravity is the attractive interaction between masses. Earth’s mass produces the force pulling nearby objects toward its centre. In free fall, gravity produces downward acceleration. Air resistance, if present, acts separately and generally opposes the falling motion.
Q23. Which symbol denotes acceleration due to gravity?
[RRB Junior Engineer — 23 May 2019, Shift 3]
(A) Lowercase g
(B) Uppercase G
(C) Greek gamma
(D) Greek epsilon
Answer: (A) Lowercase g
Explanation: Lowercase g represents gravitational acceleration, commonly around 9.8 m/s² near Earth’s surface. Capital G represents the universal gravitation constant, with different units. Confusing the two symbols leads to errors in weight and gravitational-field equations.
Q22. Where on Earth is the acceleration due to gravity generally highest?
[RRB ALP Fitter — 23 Jan 2019, Shift 2]
(A) At the poles
(B) At infinite distance
(C) At the equator
(D) At Earth’s centre
Answer: (A) At the poles
Explanation: Gravity is strongest near the poles because Earth’s radius is smaller there and rotational reduction in effective gravity is minimal. Its value is less at the equator; at the centre, the idealised net gravitational field vanishes.
Q21. If surface gravity is g, what is gravity at height R/2 above Earth’s surface?
[RPSC Senior Teacher Grade II Science — 01 Nov 2018]
(A) 0
(B) 2g/3
(C) 4g/9
(D) g/2
Answer: (C) 4g/9
Explanation: At distance R + h from Earth’s centre, gravity equals GM/(R + h)². With h = R/2, the distance becomes 3R/2. Hence the new g equals GM/(9R²/4) = 4g/9.
