JEE Physics Laws Of Motion MCQs Set 26

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Review structured MCQ sets for JEE Physics Laws Of Motion. Built according to official JEE guidelines, these downloadable questions support daily revision and core concept reinforcement.

Chapter-wise Objective Questions: Laws Of Motion

Access the complete set of multiple-choice questions for Laws Of Motion below. This focused format allows students to isolate specific topics for thorough review and uninterrupted practice alongside official JEE textbooks.

Multiple Choice Questions

Question 1: A reference frame attached to the earth
(a) is an inertial frame by definition
(b) cannot be an inertial frame because the earth is revolving round the sun
(c) is an inertial frame because Newton's laws are applicable
(d) is an inertial frame because the earth is rotating about its own axis
Show Answer & Explanation

Answer: (b) cannot be an inertial frame because the earth is revolving round the sun

Explanation:
1. The earth rotates and revolves, so it has centripetal acceleration.
2. Strictly it is therefore a non-inertial frame, though it is a very good approximation for most purposes.

Teacher's Note:
1. Accelerated or rotating frames are non-inertial.

Question 2: A person of mass 60 kg is inside a lift of mass 940 kg and presses the button on the control panel. The lift starts moving upwards with an acceleration of 1.0 m/s². If g = 10 m/s², the tension in the supporting cable is
(a) 8600 N
(b) 9680 N
(c) 11000 N
(d) 1200 N
Show Answer & Explanation

Answer: (c) 11000 N

Explanation:
1. Total mass = 1000 kg.
2. T − 1000g = 1000 × 1, so T = 1000 × 11 = 11000 N.

Teacher's Note:
1. Treat the lift and person as one system.

Question 3: A car moves at a speed of 20 m/s on a banked track and describes an arc of a circle of radius 40√3 m. The angle of banking for no friction is (g = 10 m/s²)
(a) 25°
(b) 60°
(c) 45°
(d) 30°
Show Answer & Explanation

Answer: (d) 30°

Explanation:
1. tan θ = v²/(rg) = 400/(40√3 × 10) = 1/√3.
2. So θ = 30°.

Teacher's Note:
1. tan θ = v²/rg.

Question 4: A man is standing at the centre of a frictionless pond of ice. How can he get himself to the shore?
(a) By throwing his shirt in a vertically upward direction
(b) By spitting horizontally
(c) He will wait for the ice to melt in the pond
(d) Unable to get at the shore
Show Answer & Explanation

Answer: (b) By spitting horizontally

Explanation:
1. There is no friction, so only momentum conservation can move him.
2. Spitting (or throwing something) horizontally gives him an equal and opposite momentum towards the shore.

Teacher's Note:
1. Throw something horizontally away from the shore.

Question 5: A rectangular block is placed on a rough horizontal surface first standing on its small face and then lying on its large face. The friction is
(a) more in the first case
(b) more in the second case
(c) equal in both cases
(d) dependent on the dimensions
Show Answer & Explanation

Answer: (c) equal in both cases

Explanation:
1. Friction f = μN with N = mg in both cases.
2. It does not depend on the area of contact.

Teacher's Note:
1. Area of contact does not affect friction.

Question 6: A metre scale is moving with uniform velocity. This implies
(a) the force acting on the scale is zero, but a torque about the centre of mass can act on the scale
(b) the force acting on the scale is zero and the torque acting about the centre of mass of the scale is also zero
(c) the total force acting on it need not be zero but the torque on it is zero
(d) neither the force nor the torque need to be zero
Show Answer & Explanation

Answer: (b) the force acting on the scale is zero and the torque acting about the centre of mass of the scale is also zero

Explanation:
1. Uniform velocity means no linear acceleration, so the net force is zero.
2. The scale also does not rotate with changing angular velocity, hence no net torque about the centre of mass.

Teacher's Note:
1. Both translational and rotational equilibrium hold.

Question 7: When a box is stationary relative to a train moving with acceleration, the relative motion is opposed by the ...X... friction, which gives the box the same acceleration as the train. X is
(a) kinetic
(b) static
(c) limiting
(d) none of these
Show Answer & Explanation

Answer: (b) static

Explanation:
1. There is no relative sliding, so the friction is static.
2. It provides the force that accelerates the box with the train.

Teacher's Note:
1. No sliding means static friction.

Question 8: A particle tied to a string describes a vertical circular motion of radius r continually. If it has a velocity √(3gr) at the highest point, the ratio of the respective tensions in the string holding it at the highest and lowest points is
(a) 4 : 3
(b) 5 : 4
(c) 1 : 4
(d) 3 : 2
Show Answer & Explanation

Answer: (c) 1 : 4

Explanation:
1. At the top: T₁ + mg = m(3gr)/r, so T₁ = 2mg.
2. Speed at the bottom: v² = 3gr + 4gr = 7gr, so T₂ − mg = 7mg and T₂ = 8mg.
3. T₁ : T₂ = 1 : 4.

Teacher's Note:
1. Use energy conservation between the top and the bottom.

Question 9: Which of the following expressions is correct?
(a) \( F=ma \)
(b) \( F=\frac{m}{a} \)
(c) \( F=\frac{a}{m} \)
(d) none of these
Show Answer & Explanation

Answer: (a) \( F=ma \)

Explanation:
1. Newton's second law gives F = ma.
2. The other expressions have the wrong dimensions.

Teacher's Note:
1. Check the dimensions: force is mass times acceleration.

Question 10: The coefficient of static friction between block A of mass 2 kg and the table is 0.2. Block A is connected by a light string over a smooth pulley at the edge of the table to a hanging block B. What is the maximum mass of B so that the blocks do not move? (g = 10 m/s²)
(a) 0.4 kg
(b) 2.0 kg
(c) 4.0 kg
(d) 0.2 kg
Show Answer & Explanation

Answer: (a) 0.4 kg

Explanation:
1. The maximum static friction on A = μ m_A g = 0.2 × 2 × 10 = 4 N.
2. For equilibrium m_B g ≤ 4 N, so m_B ≤ 0.4 kg.

Teacher's Note:
1. Weight of B must not exceed the limiting friction.

Question 11: A block A of mass m₁ rests on a horizontal table. A light string connected to it passes over a frictionless pulley at the edge of the table and carries a block B of mass m₂ hanging. The coefficient of kinetic friction between A and the table is μk. When A is sliding on the table, the tension in the string is
(a) \( \frac{(m_2-\mu_k m_1)g}{m_1+m_2} \)
(b) \( \frac{m_1m_2(1+\mu_k)g}{m_1+m_2} \)
(c) \( \frac{m_1m_2(1-\mu_k)g}{m_1+m_2} \)
(d) \( \frac{(m_2+\mu_k m_1)g}{m_1+m_2} \)
Show Answer & Explanation

Answer: (b) \( \frac{m_1m_2(1+\mu_k)g}{m_1+m_2} \)

Explanation:
1. a = (m₂ − μk m₁)g/(m₁ + m₂).
2. For B: T = m₂(g − a) = m₂ g[(m₁ + m₂ − m₂ + μk m₁)/(m₁ + m₂)] = m₁m₂(1 + μk)g/(m₁ + m₂).

Teacher's Note:
1. Solve for the acceleration first, then for the tension.

Question 12:
Assertion (A): A force is required to move a body uniformly along a circle.
Reason (R): When the motion is uniform, the acceleration is zero.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (c) A is true, but R is false.

Explanation:
1. Uniform circular motion needs a centripetal force, so the Assertion is true.
2. The acceleration is not zero (it is v²/r towards the centre), so the Reason is false.

Teacher's Note:
1. Uniform speed does not mean zero acceleration.

Question 13: A given object takes n times as much time to slide down a 45° rough incline as it takes to slide down a perfectly smooth 45° incline. The coefficient of kinetic friction between the object and the incline is
(a) \( \left(1-\frac{1}{n^{2}}\right) \)
(b) \( \frac{1}{1-n^{2}} \)
(c) \( \sqrt{1-\frac{1}{n^{2}}} \)
(d) \( \sqrt{\frac{1}{1-n^{2}}} \)
Show Answer & Explanation

Answer: (a) \( \left(1-\frac{1}{n^{2}}\right) \)

Explanation:
1. For the same distance, t ∝ 1/√a, so n² = a_smooth/a_rough.
2. At 45°, a_smooth = g/√2 and a_rough = (g/√2)(1 − μ), so n² = 1/(1 − μ).
3. μ = 1 − 1/n².

Teacher's Note:
1. Compare the two accelerations.

Question 14: Which of the following statements about friction is true?
(a) Friction can be reduced to zero
(b) Frictional force cannot accelerate a body
(c) Frictional force is proportional to the area of contact between the two surfaces
(d) Kinetic friction is always greater than rolling friction
Show Answer & Explanation

Answer: (d) Kinetic friction is always greater than rolling friction

Explanation:
1. Kinetic friction is always greater than rolling friction, so (d) is true.
2. Friction cannot be reduced exactly to zero, it can accelerate a body (a walking person or a car), and it is independent of area.

Teacher's Note:
1. μr < μk always.

Question 15: A ball is thrown up at an angle with the horizontal. The magnitude of the total change of momentum by the instant it returns to the ground is
(a) acceleration due to gravity × total time of flight
(b) weight of the ball × half the time of flight
(c) weight of the ball × total time of flight
(d) weight of the ball × horizontal range
Show Answer & Explanation

Answer: (c) weight of the ball × total time of flight

Explanation:
1. The only force is the weight, so Δp = mg × T (impulse-momentum theorem).
2. The change is along the vertical, equal to 2mu sin θ = mg T.

Teacher's Note:
1. Impulse of gravity over the whole flight.

Question 16: Match the columns.
Column IColumn II
(A) Unbalanced force(1) Acts on two different bodies
(B) Action and reaction(2) Inability to change the state
(C) Inertia(3) \( mv \)
(D) Momentum(4) Variable velocity

(a) A-4, B-1, C-2, D-3
(b) A-2, B-1, C-4, D-3
(c) A-4, B-1, C-3, D-2
(d) A-4, B-3, C-2, D-1
Show Answer & Explanation

Answer: (a) A-4, B-1, C-2, D-3

Explanation:
1. An unbalanced force causes acceleration, so the velocity varies.
2. Action and reaction act on two different bodies.
3. Inertia is the inability of a body to change its state by itself.
4. Momentum is mv.

Teacher's Note:
1. Match definitions with the correct term.

Question 17: A boy sitting on the topmost berth in the compartment of a train which is just going to stop at a railway station drops an apple aiming at the open hand of his brother situated vertically below his own hand at a distance of 2 m. The apple will fall
(a) in the hand of his brother
(b) slightly away from the hand of his brother in the direction of motion of the train
(c) slightly away from the hand of his brother opposite to the direction of motion of the train
(d) none of the above
Show Answer & Explanation

Answer: (b) slightly away from the hand of his brother in the direction of motion of the train

Explanation:
1. The apple keeps the train's forward velocity while the train decelerates.
2. The brother's hand slows down, so the apple lands ahead of it in the direction of motion of the train.

Teacher's Note:
1. Relative to the decelerating train, the apple drifts forward.

Question 18: Two light spring balances A and B are connected in series and a block of mass 4 kg is hung from the lower balance B, with A attached to the ceiling. The readings of A and B respectively are
(a) 4 kg and zero
(b) zero and 4 kg
(c) 4 kg and 4 kg
(d) 2 kg and 2 kg
Show Answer & Explanation

Answer: (c) 4 kg and 4 kg

Explanation:
1. The tension is the same through the light spring balances in series.
2. Each balance carries the 4 kg weight and reads 4 kg.

Teacher's Note:
1. Massless springs in series transmit the same force.

Question 19:
Assertion (A): The same force applied for the same time causes the same change in momentum for different bodies.
Reason (R): The total momentum of an isolated system of interacting bodies remains conserved.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. Δp = F Δt, independent of mass, so the Assertion is true.
2. Momentum conservation is also true but is not the reason for the Assertion.

Teacher's Note:
1. Impulse fixes the change in momentum.

Question 20: Newton's second law measures the
(a) acceleration
(b) force
(c) momentum
(d) angular momentum
Show Answer & Explanation

Answer: (b) force

Explanation:
1. The second law, F = dp/dt, gives a quantitative measure of force.
2. The first law only defines force qualitatively.

Teacher's Note:
1. The second law is the quantitative law of force.

Question 21: Choose the incorrect statement(s). I. If a body is not at rest, then the net external force acting on it cannot be zero. II. If the net force acting on a body is zero then the body will essentially remain at rest.
(a) I only
(b) II only
(c) I and II
(d) none of these
Show Answer & Explanation

Answer: (c) I and II

Explanation:
1. A body moving with constant velocity has zero net force, so I is incorrect.
2. A zero net force only means the body keeps its state, which may be uniform motion, so II is incorrect.

Teacher's Note:
1. Uniform motion also needs zero net force.

Question 22: A thin cushion of air maintained between solid surfaces is another effective way of ...... the friction opposing relative motion. The missing word is
(a) reducing
(b) increasing
(c) doubling
(d) removing the need for
Show Answer & Explanation

Answer: (a) reducing

Explanation:
1. An air cushion separates the surfaces, which reduces the friction opposing their relative motion.
2. Hovercraft and air tracks use this.

Teacher's Note:
1. Lubrication reduces friction.

Question 23:
Assertion (A): If the net external force on a body is zero, then its acceleration is zero.
Reason (R): Acceleration does not depend on force.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (c) A is true, but R is false.

Explanation:
1. F = ma gives a = 0 when F = 0, so the Assertion is true.
2. Acceleration is proportional to the net force, so the Reason is false.

Teacher's Note:
1. a = F/m.

Question 24: Newton's second and third laws of motion lead to the conservation of
(a) linear momentum
(b) angular momentum
(c) potential energy
(d) kinetic energy
Show Answer & Explanation

Answer: (a) linear momentum

Explanation:
1. For an isolated system, internal forces form action-reaction pairs and cancel.
2. The total momentum then stays constant.

Teacher's Note:
1. Conservation of linear momentum follows from the second and third laws.

Question 25: If the resultant of all the external forces acting on a system of particles is zero, then from an inertial frame one can surely say that
(a) linear momentum of the system does not change in time
(b) kinetic energy of the system does not change in time
(c) angular momentum of the system does not change in time
(d) potential energy of the system does not change in time
Show Answer & Explanation

Answer: (a) linear momentum of the system does not change in time

Explanation:
1. Zero net external force gives dP/dt = 0.
2. Torque, kinetic energy or potential energy may still change.

Teacher's Note:
1. Only linear momentum is guaranteed constant.

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Multiple Choice Questions (MCQs) for JEE Physics Laws Of Motion

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