NIOS Class 12 Physics Chapter 3 Laws of Motion

NIOS Class 12 Physics Chapter 3 Laws of Motion Solutions English Medium As Per New Syllabus to each chapter is provided in the list so that you can easily browse throughout different chapters NIOS Class 12 Physics Chapter 3 Laws of Motion Notes in English and select need one. NIOS Class 12 Physics Solutions English Medium Download PDF. NIOS Study Material of Class 12 Physics Notes Paper Code: 312.

NIOS Class 12 Physics Chapter 3 Laws of Motion

Also, you can read the NIOS book online in these sections Solutions by Expert Teachers as per National Institute of Open Schooling (NIOS) Book guidelines. These solutions are part of NIOS All Subject Solutions. Here we have given NIOS Class 12 Physics Notes, NIOS Senior Secondary Course Physics Solutions in English for All Chapter, You can practice these here.

Laws of Motion

Chapter: 3

INTEXT QUESTIONS 3.1

1. Is it correct to state that a body always moves in the direction of the net external force acting on it?

Ans: No, this statement is not always correct. A body moves in the direction of the net external force only when the body was initially at rest before the application of the force. If the body was already in motion, the net force changes the velocity but not necessarily in the direction of the force. The direction of motion depends on the resultant of the initial velocity and the change in velocity due to the applied force.

2. What physical quantity is a measure of the inertia of a body?

Ans: Mass is the physical quantity that measures the inertia of a body. Greater the mass, greater is the inertia, and more difficult it is to change the state of rest or motion of the body.

3. Can a force change only the direction of velocity of an object keeping its magnitude constant?

Ans: Yes, a force can change only the direction of velocity while keeping its magnitude constant. This happens when the force is always perpendicular to the velocity vector. The best example is uniform circular motion, where centripetal force acts perpendicular to velocity, changing only the direction but not the magnitude of velocity.

4. State the different types of changes which a force can bring in a body when applied on it.

Ans: A force can bring about the following changes in a body:

(a) Change the state of rest or uniform motion (accelerate or decelerate)

(b) Change the direction of motion

(c) Change the shape and size of the body (deformation)

(d) Cause rotation about an axis

INTEXT QUESTIONS 3.2

1. Two objects of different masses have the same momentum. Which of them is moving faster?

Ans: The object with smaller mass is moving faster.

Since momentum p = mv, 

if two objects have the same momentum:

m₁v₁ = m₂v₂

If m₁ < m₂, then v₁ > v₂

The object with smaller mass must have greater velocity to have the same momentum.

2. A boy throws up a ball with a velocity v₀. If the ball returns to the thrower with the same velocity, will there be any change in:

(a) Momentum of the ball?

(b) Magnitude of the momentum of the ball?

Ans: (a) Yes, there is a change in momentum. Initial momentum = mv₀ Final momentum = mv₀ .The change in momentum = mv₀ – (-mv₀) = 2mv₀

(b) No, the magnitude of momentum remains the same (mv₀) as the speed is the same in both cases.

3. When a ball falls from a height, its momentum increases. What causes increase in its momentum?

Ans: The gravitational force acting on the ball causes the increase in its momentum. According to Newton’s second law, F = dp/dt, the gravitational force mg acts downward, continuously changing the momentum of the ball in the downward direction.

4. In which case will there be larger change in momentum of the object?

(a) A 150 N force acts for 0.1 s on a 2 kg object initially at rest.

(b) A 150 N force acts for 0.2 s on a 2 kg object initially at rest.

Ans: Case (b) will have a larger change in momentum.

Using impulse-momentum theorem:

Δp = FΔt

Case (a): Δp = 150 × 0.1 

= 15 kg⋅m/s

Case (b): Δp = 150 × 0.2

= 30 kg⋅m/s

5. An object is moving at a constant speed in a circular path. Does the object have constant momentum? Give reason for your Answer.

Ans: No, the object does not have constant momentum. Although the speed is constant, the direction of velocity changes continuously in circular motion. Since momentum is a vector quantity (p = mv), and the direction of velocity vector changes, the momentum vector also changes continuously even though its magnitude remains constant.

INTEXT QUESTIONS 3.3

1. When a high jumper leaves the ground, where does the force which throws the jumper upwards come from?

Ans: The upward force comes from the ground. When the jumper pushes down on the ground with their legs, according to Newton’s third law, the ground exerts an equal and opposite reaction force upward on the jumper. This reaction force from the ground propels the jumper upward.

2. Identify the action-reaction forces in each of the following situations:

(a) A man kicks a football.

(b) Earth pulls the moon.

(c) A ball hits a wall.

Ans: (a) Action: Force exerted by man’s foot on the football.

Reaction: Force exerted by the football on man’s foot.

(b) Action: Gravitational force exerted by Earth on the moon.

Reaction: Gravitational force exerted by the moon on Earth.

(c) Action: Force exerted by the ball on the wall.

Reaction: Force exerted by the wall on the ball.

3. “A person exerts a large force on an almirah to push it forward but he is not pushed backward because the almirah exerts a small force on him”. Is the argument given here correct? Explain.

Ans: No, this argument is incorrect. According to Newton’s third law, the almirah exerts exactly the same magnitude of force on the person as the person exerts on the almirah. 

The person doesn’t get pushed backward because:

(i) There is sufficient friction between the person’s feet and the floor to prevent sliding The person can brace themselves against the applied force.

(ii) On a slippery surface, the person would indeed be pushed backward when trying to push the almirah.

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