JKBOSE 9th Class Science Solutions Chapter 2 Force and Laws of Motion

◆ Gallileo and Isac Newton put forth the scientific basis with regard to the motion of the objects.

◆ By applying force the motion can be given to a body at rest and the body in motion can be brought to rest or a change can be brought about in the same direction.

◆ The concept of force is based on the activity of pull, push or hit/kick.

◆ By the application of force the size and shape of an object can be changed.

◆ Force is of two types: (1) Balanced force and (ii) unbalanced force.

◆ An unbalanced force acting on an object, produces motion in the object.

◆ Frictional force acts against the direction of motion of an object.

◆ To reduce the effect of friction the surface is either made plane or the surface is painted with a lubricant.

◆ S.I. unit of force is newton.

◆ For motion of the object due to the force acting on it, Newton gave three fundamental laws of motion which hold good for all types of motion.

◆ According to first law, everybody tends to remain in its state of rest or of uniform motion unless some external force acts on it.

◆ According to second law, the rate of change of momentum of a body is directly proportional to the unbalanced force acting on it and in its direction.

◆ According to third law, when one body applies force on another body, the second body also applies instantaneous force on the first body. These two forces are equal in magnitude but opposite in direction.

◆ The first law of motion is also called the Laws of Inertia.

◆ The tendency of the body to remain in the state of rest or of uniform motion is called Inertia.

◆ Everybody opposes the change in its state of motion.

◆ The moment of inertia of train is more than that of cart so that it does not get displaced on being pushed. In other words, the heavier bodies have more inertia.

◆ The inertia of an object is the measure of its mass.

◆ The momentum ‘p’ of an object is measured by the product of its mass ‘m’ and velocity ‘v’.

                i.e.      p = m x v

◆ The momentum has both magnitude and velocity. Its direction is same as that of velocity.

◆ The S.I. unit of mometum is kg ms -¹.

◆ Force changes the momentum of an object.

⇒ Force. It is an external cause which produces or tends to produce a change in its state of rest or of uniform motion.

⇒ One Newton Force. It is the force that produces an acceleration of 1 m s-² in a body of mass 1 kg. It is denoted by ‘N’.

⇒ Balanced Forces. If number of forces acting on an object do not produce any change in its state then these forces are called Balanced Forces. Their net result zero force.

⇒ Unbalanced Forces. If the result of various forces acting on an object is not zero, then these forces are called unbalanced forces.

⇒ Frictional Force. It is the opposing force that comes into play when a body moves over the surface of another body.

⇒ Inertia. It is the property of the bodies due to which they cannot change their position of rest or of uniform motion unless some external force is applied.

⇒ Inertia of Rest. It is the property by virtue of which a body at rest will continue to remain at rest unless some external force is applied to bring about that change.

⇒ Inertia of Motion. It is the property of a body by virtue of which the body in into motion, will continue to move with same uniform speed unless some external force is applied to bring about that change.

⇒ Momentum. The product of mass and velocity possessed by a body is called its momentum.

⇒ Law of Conservation of Momentum. If no external force acts on a system of particles then the total momentum of the system remains conserved.

⇒ Newton’s First Law of Motion. If a body is at rest, it will continue to remain at rest. And if a body is moving with a uniform velocity in a straight line it will ofes continue to do so unless some external force applied to bring about that de change in its state.

⇒ Newton’s Second Law of Motion. The rate of change of momentum of a body tes is directly proportional to the applied force and takes place in the direction of site force.

⇒ Newton’s Third Law of Motion. Every action has an equal and opposite reaction.

Ans.—We know that mass of an object is the measure of its inertia. The more is the mass of an object, the more is its inertia hence.

(a) a stone of the same size has more inertia than a rubber ball.

(b) a train has more inertia than a bicycle.

(c) a rs.5 coin has more inertia than rs.1 coin because a rs.5 coin has more mass than a rs.1 coin.

Ans.— To push, to strike or to pull, all these activities act as a force for changing the velocity or for changing the direction of motion of the object. Therefore, in the above given example the velocity of ball changes four times.

(i) First time the football player of first team kicks the football to another player of his team and thus changes the velocity of the football.

(ii) In second time velocity changes when the second player kicks the football towards the goal-keeper of the opposite team and applies force on the ball.

(iii) Third time the goal-keeper pushes the ball and reduces its velocity to zero by applying force.

(iv) iv) The goal-keeper now applies a force by kicking the football towards player of his team. In this case the force increases the velocity of the football.

Ans.— Before shaking, the branch of the tree, both the branch and leaves were at rest. When we shake the branch of the tree, branch moves but the leaves remain at rest due to inertia of rest and get detached from the branch.

Ans.— When the bus is moving, whole of our body is moving forward. When brakes are applied, the lower part of our body touching the bus (e.g., feet etc.) comes to rest and upper part of the body not touching the bus continue move forward due to inertia of motion and fall in forward direction.

When the bus suddenly starts and accelerates from rest, the lower part of our body starts moving forward (accelerating) along with the bus while upper part of our body tends to remain at rest due to inertia of rest and we fall backward.

Ans.— According to Newton’s third law of motion “Action and Reaction are equal and opposite.”

The horse pulls (Action) the cart with some force in the forward direction and the cart applies equal force on the cart in the backward direction (Reaction). These two forces balance each other. When the horse pushes the ground with its feet in the backward direction with force P along OP it gets reaction R due to ground along OR in the upward direction.

This force of reaction can be resolved into two rectangular components.

(1) Vertical component ‘V’ which balances the weight mg of the horse and cart in the downward direction.

The horizontal component ‘H’ which helps to move the cart in the forward direction. The force of friction between wheels and ground acts in the backward direction but the horizontal component ‘H’ acts in the forward direction is more than the backward force of friction, it succeeds to move the cart forward

Ans.— Water is ejected from rubber hose in forward direction with a force (action), it пики exerts an equal reaction on the hose in backward direction. Due to backward reaction, fire man finds it difficult to hold the hose.

Sol.— Mass of the bullet (m₁) = 50 g = 0.05 kg

Mass of the rifle (m₂) = 4 kg

Initial velocity of the bullet (u₁) = 0

Initial velocity of the rifle (u₂) = 0

Final velocity of the bullet (v₁) = 35 m s^-1

Final velocity of the rifle (v₂) = ?

According to the law of conservation of momentum,

Total initial momentum of bullet and rifle = Total final momentum of the bullet and rifle.

∴  Final velocity of the rifle, v₂ = – 0.437 m s^-1 Ans.

Negative sign indicates that the rifle moves in a direction opposite to the direction of motion of the bullet.

Sol.—  Here, mass of first object (m₁) = 100 g

V₂ = 1.165 m s −¹ in the same direction. Ans.

Ans.— Yes, it is possible for an object to move with non-zero velocity even when net zero unbalanced force is experienced by it. In this situation the magnitude of velocity and direction will be same. As for example, in case of a rain drop falling freely with constant velocity, the weight of the drop is balanced by upthrust so to say the net unbalanced force on drop is zero.

Ans.— When a carpet is beaten with a stick, the carpet is set into motion while the dust particles due to inertia tend to remain at rest. In this way dust particles get detached from the carpet and come out of it.

Ans.— When a fast moving bus suddenly takes a turn round a sharp bend then the luggage placed on the roof of a bus gets displaced. The reason for this is that the luggage tends to remain with linear motion while an unbalanced force is applied by the engine to change the direction of the bus so that the luggage kept at the roof of the bus gets displaced. So it is advised to tie the luggage with a rope on the roof of bus.

Ans.— (c) is correct. There is a force of friction on the ball in direction opposite to that of motion.

Sol.— Here initial velocity (u) = 0

Time (t) = 20 s

Distance (s) = 400 m –

We know, S = ut + 1/2 at²

or,    a = 400/200

∴ a = 2 m s^-2

Now mass of the truck (m) = 7 tonne

= 7 × 1000 kg

Acceleration (a) = 2 m s^-2

Buy,   Force, F = m × a

= 7000 kg × 2 m s^-2

= 14000 kg – m s^-2

= 14000 N Ans.

Sol.— Here, mass of stone (m) = 1 kg

Initial velocity of stone (u) = 20 m s^-1

Distance travelled by the stone (S) = 50 m

Final velocity of stone (v) = 0 (at rest)

Force of friction between the stone and ice (F) = ?

Using v² – u² = 2as, we have

(0)² – (20)² = 2 × (a) × 50

-20 × 20 = 100 × a

a = -400/100

a = – 4 m s^-2

F = ma = 1 (- 4)

F = – 4 N

Minus sign shows the force of friction is in direction opposite to direction of motion of stone.

Sol.— Mass of the engine = 8000 kg

Mass of 5 wagons = 5 x 2000 kg

= 10,000 kg

∴ Total mass of engine and 5 wagons = 8000 kg + 10,000 kg

= 18,000 kg

Total force of engine = 40,000 N

Frictional force offered by the track= 35,000 N

(a) ∴ Net Accelerating Force (F) = Total force of engine – Frictional force of track

= 40,000 N 35,000 N

= 5000 N Ans.

(b) Acceleration of the train (a) =  Accelerating force on rail (F) / Mass of the train (m)

= 35000/18000

= 1.94 m s^-2  Ans.

(c) Force exerted by wagon 1 on wagon 2 = Net Accelerating Force – Mass of wagon x Acceleration

= 35000 – 2000 x 35 / 18

= 35000 – 3888.8

= 31111.2 N Ans.

Sol.— Here the mass of automobile (m) = 1500 kg

Acceleration of vehicle (a) = -1.7 m s^-2

Frictional Force between road and vehicle (F) = ?

We know,     F = m × a

= 1500 x (-1.7)

= – 2550 N

Backward frictional force (F) = 2550 N Ans.

Ans.— (d) is correct. Momentum = mv.

Ans.— When no acceleration is to be produced (i.e. body is to be moved with constant velocity), the net force has to be zero. Force of friction should be equal and opposite to the force applied i.e., force of friction has to be 200 N.

Sol.— Given, mass of the first object (m₁) = 1.5 kg

and mass of the second object (m₂) = m₁ = 1.5 kg

Initial velocity of the first object (u₁) = 2.5 m s^-1

Initial velocity of the second object (u₂) = -2.5 m s^-1

(Since both the objects move in the direction opposite to each other therefore velocity of first object will be taken as positive and that of the other as negative.)

Suppose after collision the velocity of the combination of two objects is ‘v’

∴ According to the law of conservation of momentum,

Total momentum before collision = Total momentum after collision

m₁ u₁ + m₂ u₂ = m₁ v + m₂ v

1.5 × 2.5 + 1.5 × (- 2.5) = (1.5 × v + 1.5 × v )

1.5 [2.5 + (- 2.5)] = (1.5 + 1.5) × v

1.5 [ 2.5 – 2.5] = 3 × v

1.5 × 0 = 3 × v

∴ v = 0 m s^-1 Ans. 

i.e. Both the objects will come to rest after collision.

Ans.— Student is justified. Friction is equal and opposite to force applied till the force applied crosses the force of limiting friction. When he applies a force slightly more than force of limiting friction, the truck will move. Till the truck moves uniformly, the force applied is exactly equal to force of friction at that instant.

 Sol.—  Mass of the ball (m) = 200 g

= 0.2 kg

Initial velocity of the ball (u) = 10 ms^-1

Final velocity of the ball (u) = -5 ms^-1

[∴ the direction of the ball is opposite to the first direction]

Change in momentum of the ball = Final momentum – Initial momentum.

= mv – mu

= m (v – u)

= 0.2 (- 5 – 10)

= 0.2 × (- 15)

= -3.0 kg-ms-¹ Ans.

Sol.— Here, mass of the object (m) = 100 kg

Initial velocity of the object (u) = 5 ms^-1

Final velocity of the object (v) = 8 ms^-1

Time interval (t) = 6s

Initial momentum of the object (p₁) = m × u

= 100 × 5

= 500 kg – ms^-1

Final momentum of the object (p₂) = m × v

= 100 × 8

= 800 kg – ms^-1

Force acting on the object (F) = P₂ – P₁ / t

= (800 – 500) kg – ms^-1 / 6s

= 50 kg – ms^-2 

= 50 N Ans.

Ans.—  I agree with Rahul’s explanation. According to law of conservation of momentum, during collision the momentum of the system (insect and motor car) remains conserved. Therefore, both insect and motor car experience the same force and hence same change in momentum. The insect having smaller mass would suffer greater change in velocity as a result of this, it will crush the insect while the motor car does not suffer any noticeable change in velocity.

(a) Table shows that the motion is accelerated and acceleration is increasing uniformly with time i.e. acceleration is increasing by 6 ms^-2 every second

(b) Since acceleration is increasing uniformly, the force is also increasing uniformly with time.

Sol.— Here, mass of the car (m) = 1200 kg

Acceleration produced in the car (a) = 0.2 ms^-2 

Acceleration = Acceleration produced by first two persons in the car = 0)

It is clear that when third person pushes the car, an unbalanced force acts on the car which produces an acceleration of 0.2 ms^-2

∴ Force applied by three persons together (F) = m × a

= 1200 x 0.2

= 240 N

Now because three persons together push the car using their muscular force to produce an acceleration of 0.2 ms^-2

∴ Push (Force) applied by each person = F/3

= 240 N / 3

= 80 N Ans.

Sol.—  Mass of the hammer (m) = 50 gm

∴ Force = 2500 N Ans.

Ans.— Types of forces. There are two types of forces :

(i) Balanced forces

(ii) Unbalanced Forces.

(i) Balanced Forces. When several forces are acting simultaneously on a body and their resultant is zero, the forces are said to be balanced forces.

In the case of balanced forces if some body is at rest then it will remain at rest and if it is moving with uniform speed then it will continue to move with the same speed, as if no force is doing any work. In this way with the effect of balanced forces. There does not take place any change in position of the body.

Balanced forces change the shape of the objects. e.g. if a rubber ball is pressed between palms by applying equal and opposite forces than the shape of the ball changes. This ball no longer remains round and instead becomes flat.

Example. In a tug of war, when both teams pull the rope with equal force, then resultant forces becomes zero. Therefore, both teams remain in their places. In this situation the forces applied by the two teams are equal and opposite so get balanced.

Two equal forces acting in the opposite direction become balanced if they act along the same line and their magnitudes are equal.

(ii) Unbalanced Forces. If the resultant of the several forces acting on a body is not zero, the forces are said to be unbalanced forces. Unbalanced forces produce change in the direction of uniform motion of the body or its state of rest.

Example : In a tug-of-war, when one of the two teams pulls the rope with a larger force, it is able to pull the weaker team towards it. Here two forces are not balanced. Therefore, it results in the motion of the weaker team towards the larger force along the rope.

Unbalanced force can also destroy the motion of a body. When a ball rolls on the ground a force of friction acts opposite to the direction of motion which makes the forces unbalanced. As a result of which the ball stops rolling after some time.

Ans.— Newton’s First Law of Motion. This law states that “In this universe all bodies will remain in their state of rest or of uniform motion in a straight line until some external force is applied to bring about change in their state.”

According to this law, motion can be divided into two parts :

(i) First part says that a body at rest continues in its state of rest unless some external

force is applied to bring change in its state of rest. We find a book lying on the table keeps lying in the same state unless someone applies force on it to pick it up. i

(ii) Second part says that a body in uniform motion continues moving in straight line path with a uniform speed unless someone applies external force to stop it. But in our daily life it appears but different.

As for example when we stop pedalling a bicycle the moving bicycle stops. After studying minutely it is found that between tyres of bicycle and ground these acts a force of friction which is an external force which opposes the motion. The resistance of air also opposes the motion of bicycle. So, moving bicycle stops moving due to these two forces.

Ans.—  Inertia. It is the property of matter by virtue of which an object is unable to change by itself its state of rest or of uniform motion in a straight line.

Because of this property Newton’s First Law of Motion is also called the law of Inertia.

Types of Inertia Inertia is of three types :

1. Inertia of Rest. It means a body at rest tends to remain in its position of rest. i.e. a body at rest opposes the forces which try to move it. It can be understood clearly by the following example.

A man standing in a stationary bus or train falls backward when the bus or train suddenly starts moving forward. When the bus moves, the lower part (limbs) of his body begins to move along with the bus while his upper-part tends remain at rest due to inertia.

2. Inertia of Motion. This means a body in motion continues to move with uniform motion in a straight line. i.e. it is the tendency of a body to remain in its state of uniform motion in a straight line.

Example (i) A person standing in moving bus falls forward when the bus suddenly stops. It is because as the bus stops the lower part of his body comes to rest along with the bus while upper part of his body continues to remain in motion due to inertia of motion.

(ii) An athelete runs for some distance before taking a jump so that his inertia of motion may help his muscular force to a longer jump.

3. Inertia of Direction. It is the property of a body which helps to maintain its direction i.e. it is inability of a body to change by itself its direction of motion.

Example. The mudguard fitted in the wheel of a bicycle to protect from mud particles and water drops sticking to its wheel leaving it tangentially.

Imagine a stone tied to the end of a thread moving in a horizontal circle. while doing so, if the thread breaks then due to inertia of direction the stone flies off tangentially in a straight line.

Ans.—Newton’s Second Law of Motion. Newton’s second Law of motion helps to calculate the force required to bring a body in motion. It consists of two parts : –

(i) The rate of change of momentum of a body is directly proportional to the applied unbalanced

force and

(ii) the change in momentum due to the external applied force takes place in the direction of force.

i.e. According to this law “the external force applied in the body is directly proportional to the product of mass of the body and the acceleration produced in the direction of force.

Explanation. When a force acts on a body, it produces change in its momentum. force is doubled then the change in momentum also gets doubled. The more the force applied, the more is the change in momentum produced. Momentum is the product of mass of the body and its velocity. Generally no change in mass occurs. Therefore, the rate of change of momentum is actually the rate of change of velocity. Thus the applied force is proportional to the acceleration.

When an external force acts on a body at rest, it begins to move in the direction of force. When force acts in the direction of motion of the body then its momentum gets increased. But when force acts in a direction opposite to the direction of motion, its momentum gets reduced.

Ans.— Newton’s third Law of Motion. This law states that “Every action has equal and opposite reaction” According to this law, there does not exist one force in isolation. Force always exists in pair i.e. forces of action and reaction always act on different bodies.

Explanation. (1) Consider two similar spring balances attached to each other through their hooks. One end of spring balance A is fastened to the fixed support. Pull the free balance B to right side. Note the readings of both the spring balances. Both end of spring will read the same as shown in fig. It is because read.

A and B pull each other in opposite direction with same force.

(2) Keep two balls A and B on a table at some distance from each other. When you push the ball. A towards B them the ball A acts on ball B. This force is represented by F_A→B. According to Newton, the ball B also reacts and applies force on ball A. This force is represented as F_B→A. If both the balls are similar then the magnitudes of action and reaction will be equal

∴              F_A→B = – F_B→A

Action and reaction forces always act in the direction opposite to each other.

Ans.— Law of Conservation of Momentum. For a system of bodies, the total vector sum of momenta of all the bodies due to mutual action and reaction remain unchanged so long external force acts on the system.”

Mathematical Derivation. Consider two rubber balls of masses m₁, m₂ and initial velocities u₁, u₂ respectivley. Let these collide and their velocities after collisions be v₁ and v₂ respectively. If A applies a force F on B for time t; B applies a force F on A for time t.

Ans.— Force. Force is an agent which (i) produces or tends to produce motion in the body (i) stops the moving body or tends to stop (iii) increases the speed of the body or tries to increase -the speed therefore, Force may be defined is as physical cause (a push or a pull) which changes or tends to change the state of rest or uniform motion or direction of motion of a body. The force exerted by the engine makes the train to move from its actual position of rest while the force exerted by the brakes slows down or stops the moving train. The force exerted on the steering wheel of a car changes its direction of motion.

Force is a vector quantity.

Units of force. The unit of force depends upon the unit of mass and acceleration. S.I. unit of force is Newton and C.G.S. unit is Dyne IN = 10⁵ Dynes

Ans.— When horse is running, both the horse and the rider are in motion. When the horse suddenly stops, the lower part of the rider and horse come in the state of rest while the upper part of the rider remains in motion so that he falls forward.

Ans.— The horse and the rider form one system. Initially both are at rest. When the horse suddenly gallops then the horse and the lower part of the rider come into motion in the forward direction while the upper part of the rider’s body tends to remain at rest. Therefore, the rider falls backward.

Ans.— While alighting from the moving bus the passenger falls forward because when the feet of the passenger touch the ground, his lower part suddenly comes to rest while the upper part still remains in motion. In this way the passenger falls forward.

Ans.— Momentum. It is defined as the quantity of motion possessed by the body. It is measured by the product of the mass and velocity of the body.

If m is the mass and the velocity of the body then, linear momentum of the body, p= mu Momentum is a vector quantity. Its direction is the same as that of the velocity. Units of Momentum. In C.G.S. system momentum is measured in g cms ^-1 while S.I. unit is kg-ms^-1

Ans.— (i) Both car and truck are going with same speed. Since the mass of the car is less than that of the truck therefore, the momentum of the car will be less than the momentum of the truck.

(ii) To stop both the car and the truck during same interval of time their momentums will become zero but due to more momentum of the truck, the change of the momentum of the truck will be more than the car. Therefore, the truck would require more force.

Ans.— If stone piece strikes window pane glass, it gets shattered while a fast moving bullet when strikes the window pane a round hole is formed. The reason is that small particles of glass around and near the hole do not move due to inertia along with the bullet and threfore, do not scatter.

Ans.— If a dirty blanket is beaten with a stick or is given a jerk then dust particles get separated from it because when we beat or give a jerk to the blanket it comes in motion but due to inertia of rest, dust particles remainded at rest and get separated and the blanket becomes dust free.

Ans.— When a fan is rotating, then because of inertia of motion it continues it rotation for some time even if we switch if off. Due to friction on resistance of air it comes to rest after few seconds.

Ans.— When bullet is not fired, then gun and bullet both are at rest, thus total momentum of both together is zero. When a bullet is fired from the gun the bullet moves with very high speed in the forward direction i.e. its momentum is very high. Now according to law of conservation of momentum, total momentum should still be zero as was before the firing of the bullet. Thus to balance the momentum of bullet in the forward direction gun recoil.

Ans.— A lot of force is needed to stop a fast moving ball. If we lower our hands while catching the ball, acceleration of the ball is decreased and we have to apply less force of stop the ball.

Ans.— Differences between balanced forces and unbalanced forces :

Balance forces	Unbalanced force
When balanced forces act simultaneously on a body then their net resultant is zero.	When unbalanced forces act simultaneously on a body then their net resultant is not zero.
Balanced forces are acting on a body which is at rest, these can not bring it in motion.	Unbalanced forces act on a body at rest, these can bring it in motion.
These forces cannot bring a change in speed or direction of the motion.	This force can bring change in the speed of direction of motion.
This force can make a change in the shape of the body.	This force can not make a change in the shape of the body.

Ans.—Refer to Long Answer Type Questions, Q. 3 Example (i) under the heading “Inertia of motion”.

Ans.—Newton’s first law of motion. This law states that “In this universe all the bodies will remain in their state of rest or uniform motion in a straight line until some external force is applied to bring about change in their state.”

Sol.— Here,  Force (F) = 12N

Mass (m) = 3 kg

Acceleration (a) = ?

We know F = m × a

12 = 3 × a

or,  a = 12/3

∴ a = 4 ms^-2 Ans.

Ans.— It is required to the pulled, pushed or kicked.

Ans.—  Due to unbalanced gravitational force.

Ans.—  An unbalanced force is required.

Ans.— Due to frictional force.

Ans.— By polishing/smearing the surface with a lubricant.

Ans.— Newton.

Ans.— Law of Inertia.

Ans.— Heavier objects have more inertia.

Ans.— The S.I. unit of momentum is kg – ms^-1

Ans.— In order to reduce friction.

Ans.— To increase inertia in order to take high leap.

Ans.— Law of conservation of momentum. The sum total of momentum of two objects before and after collision remains same unless some external force is applied.

Ans.—Due to more inertia of bus, more force is required to be applied for stopping it.

Ans.— In this activity the major part of momentum of the vehicle is transferred to the ground while the remaining part is transferred to the air molecules.

Ans.—1 kg wt = 9.8 Newtons.

Ans.— 1 newton = 0.102 kg wt.

Ans.— On mass.

Ans.— On Newton’s third law of motion.

Ans.—F = ma = constant, a = F/m

As mass is doubled, acceleration becomes half.

Ans.—Because they are acting on two different bodies.

(A) its speed always increases

(B) its velocity always increases

(C) it always falls towards the earth

(D) a force acts on it.

Ans.— (D) a force acts on it.

(A) speed of 1 m s^-1

(B) speed of 1 km s^-1

(C) acceleration of 10 m s -²

(D) acceleration of 1 m s -²

Ans.— (D) acceleration of 1 m s -²

(A) the force on the object

(B) the velocity of the object

(C) the mass of the object

(D) the inertia of the object.

Ans.— (A) the force on the object

(A) (mv)²

(B) mv²

(C) 1/2 mv²

(D) mv.

Ans.— (D) mv.

(A) Newton

(B) Dyne

(C) kg – ms^-1

(D) None of these.

(A) Scalar quantity

(B) Sometimes scalar and sometimes vector quantity

(C) Vector quantity

(D) None of these.

Ans.— (C) Vector quantity

(A) Law of momentum

(B) Law of Inertia

(C) Law of mass

(D) Law of force.

Ans.— (B) Law of Inertia

(A) Inertia

(B) Force

(C) Momentum

(D) None of these.

(A) 1 : 1

(B) 1 : 2

(C) 1 : 3

(D) 2 : 1

Ans.— (D) 2 : 1

(A) Speed

(B) Force

(C) Momentum

(D) Velocity

Ans.— (C) Momentum

(A) Force

(B) Speed

(C) Pressure

(D) Motion.

Ans.— (A) Force