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Newton’s Laws of Motion is the chapter that decides how comfortable the rest of mechanics will feel. JEE Main rarely asks the laws themselves — it asks you to draw a free body diagram under pressure and not miss a force. Lifts, inclines, strings over pulleys, friction: the physics is the same every time, and only the diagram changes. Ten questions below. Give them ten honest minutes.
What this chapter carries in JEE Main
- Usually 2 questions every year, which is 8 marks.
- Connected bodies, pulleys and lifts are asked almost every year.
- Friction and the angle of repose fill the rest.
What the syllabus says
In the syllabus (Unit 3, Laws of Motion): Force and inertia, Newton’s three laws of motion, momentum, impulse, conservation of linear momentum and its applications, equilibrium of concurrent forces, static and kinetic friction, laws of friction, rolling friction, dynamics of uniform circular motion, centripetal force, a vehicle on a level circular road and on a banked road.
Taken from the NTA syllabus for JEE Main 2027. See the full syllabus, unit by unit.
Formulas you must know by heart
| Second law | F = ma = dp/dt |
| Impulse | J = FΔt = Δp |
| Apparent weight in a lift | N = m(g ± a) |
| Static and kinetic friction | fs ≤ μsN, fk = μkN |
| Angle of repose | tanθ = μs |
| Block on a rough incline | a = g(sinθ − μcosθ) |
| Two connected blocks | a = F/(m1 + m2), T = m2a |
| Atwood machine | a = (m1 − m2)g/(m1 + m2) |
| Tension in an Atwood machine | T = 2m1m2g/(m1 + m2) |
Note that the angle of repose depends on the coefficient of friction alone. The mass of the block does not enter it at all, which is why a heavy box and a light one begin to slide at exactly the same angle.
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. A force of 10 N acts on a 5 kg block resting on a frictionless surface. Its acceleration is
- (a) 0.5 m/s2
- (b) 2 m/s2
- (c) 5 m/s2
- (d) 50 m/s2
Q2. A person of mass m stands in a lift that accelerates upward with acceleration a. The reading of the floor on them is
- (a) mg
- (b) m(g + a)
- (c) m(g − a)
- (d) zero
Q3. Blocks of 3 kg and 2 kg are joined by a string on a frictionless surface and a force of 10 N is applied to the 3 kg block. The tension in the string is
- (a) 2 N
- (b) 4 N
- (c) 6 N
- (d) 10 N
Q4. A block just begins to slide down an incline when the angle of the incline is θ. The coefficient of static friction is
- (a) sinθ
- (b) tanθ
- (c) cosθ
- (d) θ itself
Q5. A 10 kg block rests on a rough floor with μ = 0.2. Taking g = 10 m/s2, the least horizontal force needed to move it is
- (a) 2 N
- (b) 20 N
- (c) 100 N
- (d) 50 N
Q6. The two forces of a Newton’s third law pair always act
- (a) on the same body
- (b) on two different bodies
- (c) so as to cancel each other out
- (d) only when the body is in equilibrium
Q7. A person of mass 60 kg stands in a lift whose cable has snapped, so the lift falls freely. Their apparent weight is
- (a) 600 N
- (b) 60 N
- (c) zero
- (d) 1200 N
Q8. The impulse of a force is equal to the
- (a) change in the force
- (b) change in momentum
- (c) rate of change of momentum
- (d) work done
Q9. A ball of mass 0.1 kg strikes a wall at 10 m/s and rebounds with the same speed. The magnitude of the change in its momentum is
- (a) 1 N·s
- (b) 2 N·s
- (c) zero
- (d) 10 N·s
Q10. A block slides down a frictionless incline of 30°. Taking g = 10 m/s2, its acceleration is
- (a) 10 m/s2
- (b) 5 m/s2
- (c) 8.66 m/s2
- (d) 2.5 m/s2
Answer key, with a hint for each
| Q1 | (b) | a = F/m = 10/5. |
| Q2 | (b) | The floor must support the weight and also supply the upward acceleration, so the normal force rises. |
| Q3 | (b) | The pair accelerates at 10/5 = 2 m/s2, and the string has to accelerate only the 2 kg block. |
| Q4 | (b) | This is the angle of repose, where the component of weight along the slope equals the greatest static friction. |
| Q5 | (b) | f = μN = 0.2 × 10 × 10. |
| Q6 | (b) | They act on different bodies, which is why they never cancel. Forces only cancel when they act on the same body. |
| Q7 | (c) | In free fall the floor and the person fall together, so the floor pushes with no force at all. |
| Q8 | (b) | J = Δp. The rate of change of momentum is the force itself, not the impulse. |
| Q9 | (b) | From +1 kg m/s to −1 kg m/s, a change of 2. The reversal of direction is what students forget. |
| Q10 | (b) | a = g sin30° = 10 × 0.5. |
Now mark yourself honestly
JEE Main 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, 25 Physics questions are out of 100.
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 January.
The full chapter, on a clock
Ten questions tell you a little. Twenty-five tell you the truth.
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