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Rotational Motion is where a lot of NEET(UG) Physics marks are won and lost. The formulas look simple. Under a clock, with one minute a question, they stop looking simple. Below are ten questions to check whether this chapter is actually ready, with the answer key and a one-line hint for each.
What this chapter carries in NEET(UG)
- Usually 2 to 4 questions every year, which is 8 to 16 marks.
- Most of them come from moment of inertia, rolling bodies and conservation of angular momentum.
- The paper gives you about 1 minute a question. Knowing the formula is not enough. You have to reach the answer in that minute.
What the syllabus says
In the syllabus (Unit 5, Rotational Motion): Basic concepts of rotational motion, moment of a force, torque, angular momentum, conservation of angular momentum and its applications, moment of inertia, radius of gyration, moments of inertia of simple geometrical objects, the parallel and perpendicular axes theorems, equilibrium of rigid bodies, rigid body rotation and the equations of rotational motion, comparison of linear and rotational motion.
Taken from the NMC syllabus for NEET (UG) 2026, the latest one published. See the full syllabus, unit by unit.
Formulas you must know by heart
| Ring (through centre, ⊥ to plane) | I = MR2 |
| Disc (through centre, ⊥ to plane) | I = MR2/2 |
| Solid sphere (through centre) | I = 2MR2/5 |
| Hollow sphere (through centre) | I = 2MR2/3 |
| Rod (through centre, ⊥ to rod) | I = ML2/12 |
| Rod (through one end, ⊥ to rod) | I = ML2/3 |
| Radius of gyration | k = √(I / M) |
| Parallel axis | I = Icm + Md2 |
| Perpendicular axis (flat body only) | Iz = Ix + Iy |
| Torque | τ = Iα = rF sin θ |
| Angular momentum | L = Iω = mvr |
| Rolling body, total KE | KE = ½Mv2(1 + k2/R2) |
| Rolling down an incline | a = g sin θ / (1 + k2/R2) |
Notice the last one. The mass and the radius both cancel. Only the shape decides who wins the race down the slope.
Ten questions. Give yourself ten minutes.
Write your answers down before you scroll. A question you looked up is a question you have not answered.
Q1. The moment of inertia of a uniform disc of mass M and radius R, about an axis through its centre and perpendicular to its plane, is
- (a) MR²/4
- (b) MR²/2
- (c) MR²
- (d) 2MR²/5
Q2. A ring and a disc have the same mass and the same radius. Both are released from rest at the top of the same incline and roll down without slipping. Which one reaches the bottom first?
- (a) The ring
- (b) The disc
- (c) Both together
- (d) It depends on the angle of the incline
Q3. The radius of gyration of a uniform rod of length L, about an axis through its centre and perpendicular to the rod, is
- (a) L/2
- (b) L/√12
- (c) L/√3
- (d) L/12
Q4. A torque of 10 N·m acts on a body whose moment of inertia is 5 kg·m². The angular acceleration produced is
- (a) 0.5 rad/s²
- (b) 2 rad/s²
- (c) 5 rad/s²
- (d) 50 rad/s²
Q5. A wheel is rotating at 300 revolutions per minute. Its angular velocity is
- (a) 5π rad/s
- (b) 10π rad/s
- (c) 20π rad/s
- (d) 300π rad/s
Q6. A solid sphere rolls without slipping. The fraction of its total kinetic energy that is rotational is
- (a) 2/7
- (b) 2/5
- (c) 5/7
- (d) 1/2
Q7. A particle of mass m moves with speed v in a circle of radius r. Its angular momentum about the centre is
- (a) mvr
- (b) mv²r
- (c) mv/r
- (d) mvr²
Q8. A disc is rotating about its own axis with angular velocity ω. An identical disc, at rest, is gently placed on it along the same axis, and the two rotate together. The common angular velocity is
- (a) ω
- (b) ω/2
- (c) 2ω
- (d) ω/4
Q9. A constant torque of 5 N·m turns a body through an angle of 2 radians. The work done by the torque is
- (a) 2.5 J
- (b) 5 J
- (c) 10 J
- (d) 20 J
Q10. A uniform rod of mass M and length L is pivoted at one end. Its moment of inertia about that end, perpendicular to the rod, is
- (a) ML²/12
- (b) ML²/3
- (c) ML²/2
- (d) ML²
Answer key, with a hint for each
| Q1 | (b) | I = MR²/2 for a disc. The ring is the one with MR². |
| Q2 | (b) | a = g sinθ/(1 + k²/R²). Disc has k²/R² = 1/2, ring has 1. Smaller value, bigger acceleration. |
| Q3 | (b) | I = ML²/12, so k = √(I/M) = L/√12. |
| Q4 | (b) | α = τ/I = 10/5. |
| Q5 | (b) | 300 rpm = 300 × 2π/60 = 10π rad/s. About 31.4 rad/s. |
| Q6 | (a) | Rotational share = (k²/R²)/(1 + k²/R²) = (2/5)/(7/5) = 2/7. |
| Q7 | (a) | L = mvr when the velocity is perpendicular to the radius, which it is in a circle. |
| Q8 | (b) | Angular momentum is conserved: Iω = 2Iω′. The kinetic energy is not conserved here. |
| Q9 | (c) | W = τθ = 5 × 2. |
| Q10 | (b) | ML²/3 about the end. The ML²/12 value is about the centre. |
Now mark yourself honestly
NEET(UG) marks the way it marks. Use the same rule here:
- +4 for a right answer
- −1 for a wrong one
- 0 for a blank
So ten questions here are out of 40. In the real paper, 45 Physics questions are out of 180.
If you scored 32 or more, the basics of this chapter are secure. Move to harder questions, not more of these.
If you scored below 24, do not feel bad about it. You have just found out something useful before the exam did. Go back to the formula table above, learn it properly, and sit these ten again tomorrow.
And if you guessed a few and they landed, count those as wrong. A guess that works once will not work in May.
The full chapter, on a clock
Ten questions tell you a little. Forty-five tell you the truth.
The Beginner paper for Rotational Motion is waiting for you on the portal: 45 questions, 45 minutes, marked out of 180, with the answer key and a hint for every question. Sit it tonight and you will know exactly where this chapter stands.
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