System of Particles and Rotational MotionNEET MCQs with solutions
System of Particles and Rotational Motion covers centre of mass, torque, angular momentum, moment of inertia, rolling motion and the parallel/perpendicular axis theorems. NEET tests moment of inertia values, torque calculations, angular momentum conservation and rolling problems. This is one of Physics' toughest and highest-scoring chapters.
- Class
- 11 Physics
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- 24 questions
- In the RankUp app
- 535 questions
- ELITE questions
- 170
- NCERT topics
- 15
Practise 24 questions
Tap an option to check it. Questions from every NCERT topic in this chapter, from easy to hard.
Q1Grand Test
A particle of mass 2 kg is located at coordinates (2 m, 3 m). The centre of mass of this single-particle system is at:
Not quite — the answer is A.
For a single particle, the CM coincides with the particle itself. No averaging is needed; xCM = 2 m, yCM = 3 m.
Q2Linear Momentum and Conservation of Momentum
Linear momentum of a body is defined as:
Not quite — the answer is B.
p = mv by definition. Option A is force (F = ma). Option C gives impulse for constant force (J = FΔt) — not momentum itself. Option D has dimensions ML²T⁻¹, which do not match momentum (MLT⁻¹).
Q3Equilibrium of Rigid Body
A rigid body is said to be in equilibrium when:
Not quite — the answer is D.
Complete equilibrium requires ΣF=0 (translational) and Στ=0 (rotational). Option A ignores rotational equilibrium. Option C fails because a body in uniform motion is also in equilibrium.
Q4Moment of Force (Torque)
The moment of force (torque) about a point is defined as:
Not quite — the answer is C.
Torque τ = r × F is a vector (cross) product of position vector r and force F. Option D is wrong because torque uses cross product not dot product, and involves force not velocity.
Q5Moment of Inertia
Moment of inertia of a body depends upon:
Not quite — the answer is D.
I = Σmr² depends on both how mass is distributed and which axis is chosen. Two bodies with equal mass but different shapes have different moments of inertia.
Q6Centre of Mass
Two particles of masses 2 kg and 3 kg are placed at x = 0 m and x = 10 m respectively. The x-coordinate of the centre of mass is:
Not quite — the answer is C.
xCM = (2×0 + 3×10)/5 = 6 m. Option B (4 m) results from swapping mass weights; option D is the position of the heavier mass alone.
Q7Advanced Rotational Dynamics
The rotational analogue of Newton's second law is:
Not quite — the answer is C.
Net torque equals moment of inertia times angular acceleration: τ = Iα. Option D (L = Iω) gives angular momentum, not Newton's second law — it is the rotational analogue of p = mv, a different relation.
Q8Rolling Motion
For pure rolling without slipping, the relation between linear speed v of the centre of mass and angular speed ω is:
Not quite — the answer is C.
In pure rolling the contact point is instantaneously at rest, requiring v = Rω. Option A inverts the relation (ω/R has units of s⁻¹/m, not m/s). Options B and D are dimensionally wrong for speed.
Q9Theorems of Perpendicular and Parallel Axes
The perpendicular axis theorem is applicable only to:
Not quite — the answer is A.
Iz = Ix + Iy holds only for plane laminae where every mass element lies in the x-y plane. For 3D bodies, mass is distributed across all three dimensions, violating the theorem's core condition.
Q10Rotational Dynamics + Work, Power & Kinetic Energy
The rotational kinetic energy of a rigid body rotating with angular speed ω is:
Not quite — the answer is C.
K = ½Iω² is the standard formula. Option A (Iω²) omits the factor ½. Option D (Iω) is angular momentum, not energy.
Q11Standard Moments of Inertia
The standard moment of inertia of a thin ring of mass M and radius R about an axis through its centre perpendicular to its plane is:
Not quite — the answer is C.
For a ring, every mass element sits at distance R from the central axis, so I = MR². Compare: disc = MR²/2 (mass spread 0 to R); solid sphere = 2MR²/5; hollow sphere = 2MR²/3.
Q12Kinematics of Rotational Motion
The angular displacement of a rotating body is measured in:
Not quite — the answer is C.
Angular displacement is the angle swept by a rotating body; its SI unit is radian. Radian per second is the unit of angular velocity, not displacement.
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Get RankUp on Google PlayQ13Motion of Centre of Mass
According to Newton's second law for a system of particles, the acceleration of the centre of mass depends on:
Not quite — the answer is B.
Fext = MaCM. Internal forces appear in equal and opposite pairs by Newton's third law and cancel when summed over the whole system. Only the net external force determines aCM.
Q14Angular Momentum
The angular momentum of a particle about a point is defined as:
Not quite — the answer is C.
L = r × p, where r is the position vector and p is the linear momentum. Direction is given by the right-hand rule. Option D defines torque (τ = Iα), not angular momentum.
Q15Radius of Gyration
The radius of gyration k of a body is defined by the relation:
Not quite — the answer is B.
k is defined such that I = Mk², where M is total mass and I is moment of inertia about the chosen axis. Option A gives wrong dimensions; option C makes k independent of mass distribution incorrectly.
Q16Centre of Mass
For two equal masses placed at x = −4 m and x = +8 m, the centre of mass is located at:
Not quite — the answer is D.
For equal masses, COM = arithmetic mean = (−4 + 8)/2 = 2 m. Option B (0 m) is a common error from sign mishandling; option C (1 m) arises from adding without dividing correctly.
Q17Centre of Mass
A particle of mass 2 kg is at x = 2 m and another of mass 6 kg is at x = 8 m. Which statement correctly describes the location of the centre of mass?
Not quite — the answer is B.
xCM = (2×2 + 6×8)/8 = 52/8 = 6.5 m, nearer the heavier mass. Option C (x = 5 m) is the arithmetic mean — the classic trap for students who ignore mass weighting.
Q18Centre of Mass
A uniform circular ring of radius R has its centre of mass at:
Not quite — the answer is B.
By symmetry, all radial mass contributions cancel. COM lies at the geometric centre — a point with no material. This confirms COM need not coincide with any physical location of mass.
Q19Centre of Mass
How many of the following statements about centre of mass are correct? I. Centre of mass may lie outside the body. II. Centre of mass always lies on a particle of the system. III. Centre of mass depends on mass distribution. IV. Repositioning particles within a system generally changes the position of the centre of mass.
Not quite — the answer is C.
Statements I, III and IV are correct — 3 statements. Statement II is false: COM lies at the geometric centre of a uniform ring, where no particle exists. Students selecting D often overlook Statement II.
Q20Centre of Mass
For which of the following uniform bodies does the centre of mass lie at a point where NO material of the body is present?
Not quite — the answer is C.
A ring is hollow at its centre; COM lies at the geometric centre where there is no material. All other options are solid bodies whose COM lies within their material. This is a standard NEET exception-type question.
Q21Centre of Mass
A uniform rod of length 2 m has masses 2 kg and 6 kg attached at its two ends. Taking the end with the 2 kg mass as origin, the centre of mass of the system is located at:
Not quite — the answer is D.
xCM = (2×0 + 6×2)/(2+6) = 12/8 = 1.50 m. Option C (1.25 m) arises from dividing 10 by 8; option B from incorrectly using length/total mass without weighting positions.
Q22Centre of Mass
All of the following statements about centre of mass are correct EXCEPT:
Not quite — the answer is A.
Statement A is false. COM coincides with the geometric centre only for uniform, symmetric bodies. For asymmetric or non-uniform mass distributions, COM is displaced from the geometric centre.
Q23Centre of Mass
A uniform body possesses an axis of symmetry. Which statement correctly describes the location of its centre of mass?
Not quite — the answer is B.
Equal masses are symmetrically distributed on both sides of the axis, so perpendicular components cancel. COM must lie on the axis of symmetry. Option C is a trap: COM lies outside the material for hollow symmetric bodies but still on the axis.
Q24Centre of Mass
Three particles of masses 1 kg, 2 kg and 3 kg are placed at x = 0 m, x = 3 m and x = 6 m respectively. The x-coordinate of the centre of mass is:
Not quite — the answer is B.
xCM = (1×0 + 2×3 + 3×6)/6 = 24/6 = 4 m. Option A (3 m) is the unweighted midpoint; option C (4.5 m) is the arithmetic mean of positions — both ignore mass weighting.
ELITE question · AIR under 50 level
This chapter has 170 ELITE questions for students aiming at the very top. They are only in the app.
Unlock ELITE questions in the appKey Rotational Concepts
Quick revision: most questions in this chapter test these facts.
| Concept | Key Fact |
|---|---|
| Torque | τ = r × F = Iα; rotational analogue of force |
| Moment of inertia | Ring: MR²; Disc: ½MR²; Solid sphere: ⅖MR²; Hollow sphere: ⅔MR² |
| Angular momentum | L = Iω; conserved when net external torque = 0 |
| Parallel axis theorem | I = I_cm + Md²; shifts axis parallel to CM axis |
| Perpendicular axis theorem | I_z = I_x + I_y; for planar bodies only |
| Rolling | v_cm = Rω (pure rolling); KE = ½mv² + ½Iω² |
What the app covers in this chapter
535 questions in total, each with a detailed explanation.
| Grand Test | 58 |
| Linear Momentum and Conservation of Momentum | 39 |
| Equilibrium of Rigid Body | 39 |
| Moment of Force (Torque) | 39 |
| Moment of Inertia | 39 |
| Centre of Mass | 37 |
| Advanced Rotational Dynamics | 37 |
| Rolling Motion | 37 |
| Theorems of Perpendicular and Parallel Axes | 36 |
| Rotational Dynamics + Work, Power & Kinetic Energy | 36 |
| Standard Moments of Inertia | 35 |
| Kinematics of Rotational Motion | 35 |
| Motion of Centre of Mass | 29 |
| Angular Momentum | 20 |
| Radius of Gyration | 19 |
Questions students ask
Is Rotational Motion important for NEET?
Very important — it is one of the highest-weightage Physics chapters. Moment of inertia, torque, angular momentum conservation and rolling motion problems appear every year.
Which topics should I revise first?
Memorise MOI for all standard bodies, master the parallel and perpendicular axis theorems, angular momentum conservation problems, and rolling motion energy calculations.
How many questions from this chapter are on RankUp?
The RankUp app has 535 questions on System of Particles and Rotational Motion, including 170 ELITE questions. Every question has a detailed explanation.
