Lesson–4 : Laws of Motion

Stage–3 (Part–II) : Advanced Intermediate Questions & Numericals

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🔹 PART–F : CONCEPTUAL QUESTIONS (3–4 Marks)

1. Why is Newton’s First Law called the Law of Inertia?

Newton’s First Law explains the natural tendency of a body to resist any change in its state of rest or uniform motion. This tendency is called inertia. Hence, the first law is known as the law of inertia.

2. Can a body move with constant velocity when no force acts on it?

Yes. According to Newton’s First Law, if no external unbalanced force acts on a body, it will continue to move with uniform velocity in a straight line.

3. Why does a heavier body have more inertia?

Inertia depends on mass. A heavier body has greater mass and hence offers more resistance to change in its state of motion.

4. Why does a cricketer pull his hands backward while catching a ball?

Pulling hands backward increases the time of contact, thereby reducing the force of impact. This prevents injury to the hands.

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🔹 PART–G : REASONING QUESTIONS (IMPORTANT)

1. A passenger standing in a bus falls backward when the bus starts suddenly. Why?

Due to inertia of rest, the passenger’s body tends to remain at rest while the bus moves forward, causing him to fall backward.

2. Why does dust come out when a carpet is beaten?

Dust particles possess inertia of rest. When the carpet is beaten, the carpet moves suddenly but dust tends to remain at rest and falls off.

3. Why do action and reaction forces not cancel each other?

Action and reaction forces act on different bodies, so they cannot cancel each other.

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🔹 PART–H : NUMERICAL PROBLEMS (STEP-BY-STEP)

1. A body of mass 10 kg is acted upon by a force of 50 N. Find the acceleration produced.

Given:
m = 10 kg, F = 50 N

Solution:

a = F / m = 50 / 10 = 5 m/s²

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2. A force of 30 N acts on a body for 0.5 s. Find the impulse produced.

Solution:

Impulse = F × t = 30 × 0.5 = 15 N s

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3. A body of mass 4 kg is moving with velocity 6 m/s. Calculate its momentum.

Solution:

p = mv = 4 × 6 = 24 kg m s⁻¹

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4. A man of mass 70 kg stands in a lift accelerating upward at 1 m/s². Find the normal reaction. (g = 10 m/s²)

Solution:

N = m(g + a) = 70(10 + 1) = 770 N

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5. A force produces an acceleration of 4 m/s² in a body of mass 5 kg. Find the magnitude of the force.

Solution:

F = ma = 5 × 4 = 20 N

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🔹 PART–I : COMMON EXAM MISTAKES (AVOID THESE)

• Forgetting to draw Free Body Diagram
• Using wrong sign for acceleration in lift problems
• Mixing up action and reaction forces
• Skipping units in final answer

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🔹 PART–J : BOARD EXAM STRATEGY

• Write definitions exactly as per textbook language
• Show formula, substitution, and final answer clearly
• Numericals fetch full marks if steps are shown
• Neat presentation matters

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Stage–3 (Part–II) Completed ✔
Next: Stage–4 (IIT JEE Concepts – Bridge to Advanced Level)