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When a gun is fired it exerts forward force on the bullet. The bullet exerts an equal and opposite reaction force on the gun. This results in the recoil of the gun.

When we pull the rope downwards, an upward reaction helps us to rise up.

Here, l₁ + l₂

= (25.2 ± 0.1) + (16.8 ± 0.1)

= 42.0 ± 0.2 cm.

(a) The reading in the balance is 20 kg.  (b) Yes, if the balance is heavy the reading will change because the tension in the string will change. (c) When the blocks are of unequal masses, there will be net force on the system and it will start to move if the pulleys are friction-less. The tension in the string will change and so will be the reading of the balance. 

Action and reaction forces do not cancel each other because they act on different objects.

For every action, there is an equal and opposite reaction.

A frame in which an observer is situated and makes his observations is known as his ‘Frame of reference’. It is associated with a co-ordinate system. 

Frame of reference are of two types : 

(i) Inertial frame of reference 

(ii) Non-inertial frame of reference. 

Inertia are of three types : 

Inertia of rest, 

Inertia of motion, 

Inertia of direction.

C) Mass of the object

A) inertia of an object depends upon its mass

1. Mass is the amount of matter contained in a body while weight is the gravitational force acting on a body. 

2. Mass of body remains same while weight of body varies from place to place. 

3. Mass is a scalar but weight is a vector. 

4. Unit of mass is kilogram and that of weight is newton. 

5. Mass is measured using a physical balance and weight is measured using a spring balance.

A) A non – zero force acted on it

Correct option is C) mv

Consider a body of mass ‘m’ moving with a velocity ‘u’. Let a constant force ‘F’ applied on a body changes its velocity to V in ‘t’ seconds.

Initial momentum of the body = mass × initial velocity = m u

Final momentum = mass × Final velocity = m v

Change of momentum in ‘t’ seconds = mv – mu.

= \(\frac {mv-mu}{t}\)= m \((\frac{v-u}{t})\)

∴ α = ma

∵ \((\frac{v-u}{t})\) = a, acceleration.

According to Newton’s second law, the rate of change of momentum is directly proportional to the applied force or vice versa.

i. e. Force a rate of change of momentum

F α ma

F = kma

Where ‘k’ is a proportionality constant. 

In SI system k = 1.

∴ F = ma.

D) Both A & B

C) Newton’s third law

C) equilibrium

Correct option is D) inertia

A) equilibrium

Correct option is B) Inertia

Correct option is C) A or B

B) Newton’s second law of motion

Correct option is: (D) zero

Mass of the ball (m) = 6.0 kg 

Velocity of the ball (v) = 2.2 m/s

Momentum (p) = nv = 6.0 kg × 2.2 m/s = 13.2 kg m/s (or) 13.2 N-s

Mass: The quantity of matter present in a body is known as its mass.

Mass of the object (m) = 0.7 kg.; Acceleration (a) = 3 m/sec² 

Force required (F) = ? 

F = ma = 0.7 x 3 = 2.1 N

B) Newton’s second law of motion

Action and reaction do not balance each other because a force of action and reaction acts always on two different bodies. 

The net force Fnet = ma. SI unit of force is Kg-m/sec² or ‘Newton’.

Correct option is C) impulse

D) hitting of a ball to the body

Mass is a property of an object that specifies how much inertia the object has. SI unit of mass is the kilogram (kg).

Inertia: Inertia is a property of matter that resists changes in its state of motion or rest. It depends on the mass of the object.

Correct option is C) power

The velocity of a body is given by the distance covered by it in unit time in a given direction.-True

Uniform acceleration means that the body is moving with a uniform velocity.- False

Laws of motion: Sir Isaac Newton proposed his fundamental laws which explain the connection between force and a change in motion. These three laws are popularly called Newton’s laws of motion.

A system is said to be isolated when the net external force acting on it is zero.

Correct option is: (b) Rest

When the velocity of a body increases, acceleration is said to be positive acceleration.

Third Law of Motion: If an object exerts a force on the other object, the second object also exerts a force on the first one which is equal in magnitude but opposite in direction.

There exists no single isolated force, according to Newton’s third law of motion.

From the question we know that the block is in equilibrium 

so when we resolve the angle the force F makes with the horizontal we get Fcos60 is the force that keeps the block in equilibrium against the 100N force ,so

100N=Fcos60

100N=F/2

Therefore F=200N

The normal force or normal reaction is again got got by resolving F

N_r=Fsin60(where N_r is the normal reaction)

N_r=200(√3)/2

N_r=100(√3)N

No, external force is not required to keep a body in uniform motion.

If there is no friction, no eternal force is required to keep a body in uniform motion?

Correct option is: (A) zero

No,There is no force needed to keep a body moving with uniform velocity.

1. The coin and the paper are in inertia of rest. 

2. When we give a quick push to the paper, paper comes to inertia of motion and the coin remains in its original state i.e., inertia of rest. 

3. As a result, the paper will come out and the coin remains on the table without changing its position.

When a large force acts on a body for a short time, then the measure of the total effect of force is called impulse of force. It can be found out Impulse = Force × Time = \(\vec{F}_{av}\) × ∆t

From the principle, in an isolated system, the vector sum of the linear momentum of all bodies of the system is conserved and is unaffected du their mutual action and reaction.

The total linear momentum of all the bodies in the system is given by

\(\vec{p}=m_1\vec{v_1}+m_2\vec{v_2}+...+m_n\vec{v_n}\) = \(M\vec{v_{c.m}}=constant\)

Because they act on different bodies.