Laws of Motion - NEET Physics Questions
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Laws of Motion

Question 91: easy

Match entries in Column-I with entries in Column-II and choose the correct option.

\(\begin{array}{|l|l|} \hline \text{Column-I} & \text{Column-II} \\[0.5ex] \hline \text{A. Limiting friction} & \text{P. Has magnitude } \mu_k N \\[0.5ex] \text{B. Static friction} & \text{Q. Maximum value of static friction} \\[0.5ex] \text{C. Kinetic friction} & \text{R. Is a self adjusting force} \\[0.5ex] \hline \end{array}\)

1. A \(\rightarrow\) P, B \(\rightarrow\) Q, C \(\rightarrow\) R
2. A \(\rightarrow\) R, B \(\rightarrow\) P, C \(\rightarrow\) Q
3. A \(\rightarrow\) Q, B \(\rightarrow\) R, C \(\rightarrow\) P
4. A \(\rightarrow\) Q, B \(\rightarrow\) P, C \(\rightarrow\) R
View Answer

Limiting friction is the maximum value of static friction (A \(\rightarrow\) Q). Static friction is a self-adjusting force (B \(\rightarrow\) R). Kinetic friction has a constant magnitude of \(\mu_k N\) (C \(\rightarrow\) P).

Question 92: easy

If a cloth covers a table and some dishes are kept on it, then the cloth can be pulled out without dislodging the dishes from the table by pulling the cloth suddenly. The dishes will remain on table due to

1. Work-energy theorem
2. For every action, there is an equal and opposite reaction
3. Inertia of motion
4. Inertia of rest
View Answer

According to Newton's First Law, when the cloth is suddenly pulled, the dishes tend to maintain their state of rest due to the inertia of rest.

Question 93: easy

Assertion (A): A reference frame attached to the earth is an inertial frame of reference.


Reason (R): In practical, Newton’s laws can be applied in a frame of reference. Which is attached to the earth.


 

1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer

Assertion (A) is false. The Earth rotates and revolves, making a frame attached to it non-inertial. Reason (R) is false. Newton's laws in their original form are only valid in inertial frames. For a frame attached to the Earth, pseudo forces must be introduced to apply Newton's laws. Thus, both the Assertion and the Reason are false.

Question 94: easy

Assertion (A): An observer confined to a windowless box cannot tell by any experiment whether he is stationary or in uniform motion with constant velocity w.r.t. the fixed stars.


Reason (R): The basic laws of Physics are identical in all reference systems that move with uniform velocity w.r.t. one another.


 

1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer

Assertion (A) is true. This is a fundamental statement of the Galilean principle of relativity. Reason (R) is true. The laws of physics are invariant in all inertial frames of reference. (R) correctly explains (A) because if physical laws are identical in all inertial frames, no internal experiment can distinguish between them.

Question 95: easy

Assertion (A): According to Newton’s third law of motion, action and reaction forces are equal in magnitude and opposite in direction.


Reason (R): Net force on a body due to action-reaction pair is always equal to zero.


 

1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer

Assertion (A) is true: Newton's third law states that action and reaction forces are always equal in \(magnitude\) and opposite in \(direction\).nReason (R) is false: Action and reaction forces act on *different* bodies, so they cannot cancel each other out to produce a net force of \(0\) on a *single* body. Therefore, (A) is true but (R) is false.

Question 96: easy

Assertion (A): For an upward moving elevator (Lift), pseudo force on a block may be downward.


Reason (R): Pseudo force is the force applied by lift on block in opposite direction of motion.


 

1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer

Assertion (A) is true: When an elevator accelerates upwards with acceleration \(a\), the pseudo force on an object inside is \(ma\) downwards (in the non-inertial frame). So, for upward accelerating elevator, pseudo force on a block is downward.nReason (R) is false: Pseudo force is not a real force applied by the lift; it is an inertial force experienced in a non-inertial reference frame, acting opposite to the acceleration of the frame, not necessarily the direction of motion. Therefore, (A) is true but (R) is false.

Question 97: easy

Assertion (A): When a person walks on a rough surface, the net force exerted by surface on the person is in the direction of his motion.


Reason (R): Friction force by road on person is against motion.


 

1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer

Assertion (A) is true: To walk, a person pushes backward on the ground. By Newton's third law, the ground exerts a forward static friction force on the person's feet. This forward friction, combined with the normal force, creates a net force from the surface in the direction of motion, propelling the person forward.nReason (R) is false: For walking, the friction force exerted by the road on the person's feet is *in the direction* of the person's motion (forward friction), enabling propulsion. If friction were against the person's motion, walking would be impossible. Therefore, (A) is true but (R) is false.

Question 98: easy

A moongphaliwala sells his moongphali using a weighing machine in an elevator.


Assertion (A): He gains more profit if the elevator is accelerating up.


Reason (R): The apparent weight of an object increases in an elevator while accelerating upward.

1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer

Assertion (A) is true: If the elevator accelerates upwards, the apparent weight \(N = m(g+a)\) of the peanuts increases. If the moongphaliwala sells by the apparent weight reading (e.g., "1 kg" on the scale), they would be selling a *smaller actual mass* \(m_text{actual} = N/(g+a)\) for the same indicated weight. Thus, they gain more profit.


Reason (R) is true: When an elevator accelerates upwards, the normal force (apparent weight) on an object of mass \(m\) is \(N = m(g+a)\), which is greater than its actual weight \(mg\). Reason (R) correctly explains why the apparent weight increases, leading to the profit gain described in (A).

Question 99: easy

Assertion (A): The driver of a moving car sees a wall in front of him. To avoid collision, he should apply brakes rather than taking a turn away from the wall.


Reason (R): Friction force is needed to stop the car or taking a turn on a horizontal road.


 

1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer

Assertion (A) is true: In an emergency, applying brakes in a straight line is generally a safer and more controlled maneuver to reduce speed and avoid collision, as sudden turns at high speed can lead to loss of control or skidding.


Reason (R) is true: Both stopping the car (through braking) and taking a turn (requiring centripetal force) on a horizontal road fundamentally rely on the friction force between the tires and the road. Reason (R) is true, but it does not explain *why* braking is preferred over turning; it merely states that friction is involved in both actions.


Therefore, (A) and (R) are true, but (R) is not the correct explanation of (A).

Question 100: easy

Assertion (A): A bird sits on a stretched wire depressing it slightly. The increase in tension of the wire is more than the weight of the bird.


Reason (R): The tension must be more than the weight as it is required to balance weight.

1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer

Assertion (A) is true: When a bird sits on a wire, causing it to sag slightly, the vertical components of tension in the two halves of the wire balance the bird's weight. Since the sag is slight, the angle the wire makes with the horizontal is small. To have vertical components sum up to the bird's weight \(W\), the tension \(T\) in each part of the wire must be much larger than \(W/2\) (specifically, if \(theta\) is the angle, \(2Tsin(theta) = W\)). Given \(sin(theta)\) is small, \(T\) must be large, often significantly more than \(W\).nReason (R) is true: As explained, for the small vertical components of tension to balance the bird's weight, the overall tension in the wire must be considerably larger than the weight itself. Reason (R) correctly explains why this phenomenon occurs. Therefore, (A) and (R) are true, and (R) is the correct explanation of (A).