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#	Question	Answer
1	What is the flaw in Aristotle's argument about the force required for motion?	He did not account for frictional and viscous forces that oppose motion. In the absence of these forces, no external force is needed to maintain uniform motion.
2	How can Newton's first law be expressed in terms of acceleration?	If the net external force on a body is zero, its acceleration is zero. Acceleration can be non-zero only if there is a net external force on the body.
3	Why is a book at rest on a table not moving even though gravity acts on it?	The normal force exerted by the table on the book is equal and opposite to its weight, so the net external force is zero.
4	Why is a greater force needed to stop a heavy body than a light body in the same time if both have the same speed?	Because the heavy body has greater momentum, and the change in momentum is greater.
5	What is the mathematical form of Newton's second law for a body of constant mass?	\( \mathbf{F} = m\mathbf{a} \).
6	What is an impulsive force?	A large force that acts for a very short duration to produce a finite change in momentum.
7	What is an isolated system?	A system on which no external force acts.
8	What is the condition for equilibrium under three concurrent forces?	The vector sum of the three forces is zero. They can be represented by the sides of a closed triangle.
9	What is the maximum value of static friction?	\( (f_s)_{\max} = \mu_s N \), where \( \mu_s \) is the coefficient of static friction and \( N \) is the normal force.
10	What is rolling friction?	The resistance to motion experienced by a body rolling on a surface. It is much smaller than static or kinetic friction.
11	What provides the centripetal force for a car taking a turn on a level road?	Static friction between the tyres and the road.
12	What is a free-body diagram?	A diagram that shows a chosen system and all the forces acting on it due to the remaining parts of the assembly and other agencies. Forces exerted by the system on the environment are not included.
13	What is the SI unit of impulse?	Newton-second (N s) or kg m s⁻¹.
14	Is the equality \( mg = R \) for a body on a table a consequence of Newton's third law?	No. It is true only when the body is in equilibrium. The two forces act on the same body and are not an action-reaction pair.
15	A constant retarding force of 50 N is applied to a body of mass 20 kg moving at 15 m s⁻¹. How long does it take to stop?	6 s.
16	A shell of mass 0.020 kg is fired from a gun of mass 100 kg with a muzzle speed of 80 m s⁻¹. What is the recoil speed of the gun?	\( 0.016\,\mathrm{m\,s^{-1}} \).
17	A particle's motion is described by \( y = ut + \frac{1}{2}gt^2 \). What force acts on the particle (mass \( m \))?	\( F = mg \) — this equation describes motion under acceleration due to gravity.
18	A 3 kg block hangs by a string over a frictionless pulley connected to a 20 kg trolley on a surface with \( \mu_k = 0.04 \) (g = 10 m s⁻²). What is the acceleration of the system?	≈0.96 m s⁻² ( \( 22/23\,\mathrm{m\,s^{-2}} \) ).
19	A 2 kg wooden block rests on a soft floor. What force does the block exert on the floor (g = 10 m s⁻²)?	20 N vertically downward (equal to the block's weight, by Newton's first and third laws).
20	The same 0.1 kg stone instead lies on the floor of a train accelerating at 1 m s⁻², remaining at rest relative to the train. What is the net force on it?	0.1 N, horizontal, in the direction of the train's acceleration — provided by friction between the stone and the floor.
21	A truck starts from rest and accelerates uniformly at 2.0 m s⁻². At t=10s, a stone is dropped from the top of the truck (6 m high). What is the stone's velocity 1 s later (t=11s)?	≈22.4 m s⁻¹, about 27° below the horizontal (horizontal component 20 m s⁻¹, retained from the truck's velocity at release; vertical component 10 m s⁻¹ from free fall).
22	A position-time graph of a 4 kg particle is zero for t<0, rises linearly from 0 to 3 m between t=0 and t=4s, then stays constant at 3 m for t>4s. What is the force on the particle for t<0, for 04s?	Zero in all three intervals — the velocity is constant (0, then 0.75 m s⁻¹, then 0) within each, so there is no acceleration.
23	A batsman deflects a ball by 45° without changing its initial speed of 54 km/h (mass 0.15 kg). What is the magnitude of the impulse imparted to the ball?	≈1.72 N s ( \( = 2mv\sin(22.5°) \), using \( mv = 0.15 \times 15 = 2.25\,\mathrm{kg\,m\,s^{-1}} \) ).
24	What Sanskrit term did ancient Indian thinkers use for a body's tendency to move in a straight line, and which modern concept does it most closely resemble?	Vega — it comes closest among ancient ideas to the modern concept of inertia.
25	(NEET 2024) A 5 kg block rests on a 30° incline where \( \mu_s = 0.4 \). Will the block slide?	Yes — since \( \tan30° \approx 0.577 \) exceeds \( \mu_s = 0.4 \), the required static friction exceeds the maximum available (\( \tan\theta_{\max}=\mu_s \)).