# Samacheer Kalvi 10th Science Solutions Chapter 1 Pdf

## Samacheer Kalvi 10th Science Solutions Chapter 1 Pdf

Tamilnadu Board Samacheer Kalvi 10th Science Solutions Chapter 1: Tamilnadu State Board Solution Class 10 Science Chapter 1 – Laws of Motion.

### Samacheer Kalvi 10th Science Solutions Chapter 1: Overview

 Board Samacheer Kalvi Class 10 Subject Science Chapter 1 Chapter Name Laws of Motion

### Samacheer Kalvi 10th Science Solutions Chapter 1 Pdf

CHAPTER 1 : LAWS AND MOTION

1) Inertia of a body depends on

a) Weight of the object

b) Acceleration due to gravity of the planet

c) Mass of the object

d) Both a & b

Ans:c) Mass of the object

Explanation: Because, inertia is the property of the object depending on mass of the object only. Since acceleration due to gravity will be same on the particular planet.

2) Impulse is equals to

a) Rate of change of momentum

b) Rate of force and time

c) Change of momentum

d) Rate of change of mass

Ans:c) Change of momentum

Explanation: Because, impulse is due the change in force of the body and hence change in momentum.

3) Newton’s III law is applicable

a) For a body is at rest

b) For a body in motion

c) Both a & b

d) Only for bodies with equal masses

Ans:c) Both a & b

Explanation: Because. Newton’s third law is applicable to both body in motion and also for body at rest.

4)  Plotting a graph for momentum on the

Y-axis and time on X-axis. Slope of momentum-time graph gives

a) Impulsive force

b) Acceleration

c) Force

d) Rate of force

Ans:c) Force

Explanation: Because, rate of change of momentum is nothing but the force acting on a body.

5)  In which of the following sport the turning of effect of force used

a) Swimming

b) Tennis

c) Cycling

d) Hockey

Ans:c) Cycling

Explanation: Because, in cycling we have to apply the force on the two pedals of the cycle which forms the couple and hence gives turning effect.

6)  The unit of ‘g’ is m s-2. It can be also expressed as

a) cms-1

b) Nkg-1

c) Nm2kg-1

d) cm2s-2

Ans:b) Nkg-1

Because, F= m*a

If a= g then, F= m*g

Thus, g = F/m which is in N/kg.

7) One kilogram force equals to

a) 9.8 dyne

b) 9.8 × 104 N

c) 98 × 104 dyne

d) 980 dyne

Ans:c) 98 × 104 dyne

Because, 1N = 105 dyne

Hence, 1kg force = 98 * 104 dyne

8)  The mass of a body is measured on planet Earth as M kg. When it is taken to a planet of radius half that of the Earth then its value will be____kg

a) 4 M

b) 2M

c) M/4

d) M

Ans:d) M

Explanation: Because, the mass of the body remains same anywhere.

9)  If the Earth shrinks to 50% of its real radius its mass remaining the same, the weight of a body on the Earth will

a) Decrease by 50%

b) Increase by 50%

c) decrease by 25%

d) Increase by 300%

Ans:c) decrease by 25%

10)  To project the rockets which of the following principle(s) is / (are) required?

a) Newton’s third law of motion

b) Newton’s law of gravitation

c) Law of conservation of linear momentum

d) Both a and c

Ans:d) Both a and c

II.) Fill in the blanks

1) To produce a displacement ___________ is required

Ans:To produce a displacement forceis required

2) Passengers lean forward when sudden brake is applied in a moving vehicle. This can be explained by ___________

Ans:Passengers lean forward when sudden brake is applied in a moving vehicle. This can be explained by the inertia of motion.

3) By convention, the clockwise moments are taken as ___________ and the anticlockwise moments are taken as__________

Ans:By convention, the clockwise moments are taken as negativeand the anticlockwise moments are taken aspositive.

4) ___________ is used to change the speed of car.

Ans: Acceleration is used to change the speed of car.

5) A man of mass 100 kg has a weight of ___________ at the surface of the Earth

Ans:A man of mass 100 kg has a weight of 980 N at the surface of the Earth

III.) State whether the following statements are true or false. Correct the statement if it is false

1) The linear momentum of a system of particles is always conserved.

Ans: False

Correct statement: The linear momentum of a system of particles is always conserved when there is no external force acting on it.

2) Apparent weight of a person is always equal to his actual weight

Ans: True

3) Weight of a body is greater at the equator and less at the polar region.

Ans: False

Correct statement: Weight of the body is less at the equator and greater at the polar region.

4) Turning a nut with a spanner having a short handle is so easy than one with a long handle.

Ans: False

Correct statement: turning a nut with a spanner having a short handle is harder than one with a long handle.

5) There is no gravity in the orbiting space station around the Earth. So the astronauts feel weightlessness.

Ans: False

Correct statement: the astronauts feels weightlessness because both astronaut and space station are having the same acceleration and there is gravity in the orbiting space station around the earth also.

IV.) Match the following

Ans:

1) Newton’s First law: Stable equilibrium of body

2) Newton’s Second law: Law of force

3) Newton’s Third law: Flying nature of bird

4) Law of conservation of linear momentum: propulsion of rocket

V.) Assertion & Reasoning Mark the correct choice as

(a) If both the assertion and the reason are true and the reason is the correct explanation of assertion. (b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.

(c) Assertion is true, but the reason is false.

(d) Assertion is false, but the reason is true.

1) Assertion: The sum of the clockwise moments is equal to the sum of the anticlockwise moments.  Reason: The principle of conservation of momentum is valid if the external force on the system is zero.

Ans: (b) if both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.

2) Assertion: The value of ‘g’ decreases as height and depth increases from the surface of the Earth.  Reason: ‘g’ depends on the mass of the object and the Earth.

Ans: (c) Assertion is true, but the reason is false.

1) Define inertia. Give its classification.

Ans:

Inertia is the property of a body due to which it resist the change in its state of rest or the state of motion, unless the external unbalanced force is applied on it.

The classification of inertia is as given below:

1) Inertia of rest:

It is the resistance offered by the body when we have to change state of rest of that body.

2) Inertia of motion:

It is the resistance offered by the body when we have to change state of motion of that body.

3) Inertia of direction:

It is the resistance offered by the body when we have to change the direction of motion of that body.

2) Classify the types of force based on their application.

Ans:

The types of force based on their application are as follows:

1) Like parallel forces:

The two or more forces which are equal or unequal in magnitude but having the same direction or parallel to each other are called as like parallel forces.

2) Unlike parallel forces:

The two or more forces which are equal or unequal in magnitude but having the opposite directions or antiparallel to each other are called as unlike parallel forces.

3) If a 5 N and a 15 N forces are acting opposite to one another.  Find the resultant force and the direction of action of the resultant force

Ans:

Here the forces are having different magnitudes and opposite directions hence these are the unlike parallel forces.

Let, F1= 5N and F2= 15N

Hence, resultant force= F1 – F2

Since, F1 and F2 are in opposite directions.

Resultant force= 5 – 15 = -10N

Negative sign indicates that the resultant force -10N, acts along the direction of force F2.

4) Differentiate mass and weight.

Ans:

Mass:

• Mass is the amount of quantity present inside the body.
• Mass is the scalar quantity.
• The SI unit of mass is Kg.
• The mass of the body is constant anywhere.

Weight:

• Weight is the gravitational force acting on the body due to the earth’s gravity.
• Weight is the vector quantity.
• The SI unit of weight is N.
• The weight of the body is changes as the gravity changes.

5) Define moment of a couple.

Ans:

Moment of couple:

Moment of couple of the body is the rotation produced in body because of the couple.

Spinning top is the example of the moment of couple.

It is given by,

Moment of couple= Force* Perpendicular distance between the two lines of force acting

M= F*S

The SI unit of moment of couple is Nm.

6) State the principle of moments.

Ans:

Principle of moments:

When the many number of like or unlike or both forces acting on a body and the body is still in equilibrium then the algebraic sum of all the forces acting on the body will be zero.

7) State Newton’s second law.

Ans:

Newton’s second law of motion:

According to Newton’s second law of motion, the force acting on the body is directly proportional to the rate of change in linear momentum of the body and the direction of change in momentum is in the direction of force applied.

8) Why a spanner with a long handle is preferred to tighten screws in heavy vehicles?

Ans:

The process of tightening the screw is due to the rotating effect of couple.

And we know that, the moment of couple depends on the perpendicular distance between the two forces applied from the axis of rotation.

Hence, more the distance more is the moment of couple, force required to turn is less and hence turning effect is more.

If the spinner with long handle is preferred then due to which the force required will be less and screw is easily tighten.

9) While catching a cricket ball the fielder lowers his hands backwards.  Why?

Ans:

Because, the work of fielder is to stop the ball. When the fielder lowers his hands backward due to which the time of collision is increased thereby decreasing the retardation.

As a result retarding force decreases due to lowering of hands in backwards and hence the palm of fielder is not hurted too much.

Thus, the main aim of lowering hands backwards by fielder is to decrease the pain of palm while catching the ball.

10) How does an astronaut float in a space shuttle?

Ans:

When the apparent weight of the body is zero then that condition is called as weightlessness.

Astronaut are freely falling around the earth because of their huge orbital velocity. Also, space station and astronaut are having the same acceleration towards the earth. That means they are under the free fall condition, and both are in the same state of weightlessness.

Hence astronauts are freely falling not floating in a space shuttle.

VII.) Solve the given problems

1) Two bodies have a mass ratio of 3:4 the force applied on the bigger mass produces an acceleration of 12 ms-2.What could be the acceleration of the other body, if the same force acts on it.

Ans:

Given that, mass ratio of two bodies= m1:m2 = 3:4

Acceleration due to bigger mass is a2= 12 m/s2

And the force acting on both the body is same, let it be F.

Then, force on first body= F= m1 a1

Force on second body = F= m2 a2

Hence,                    m1 a1= m2 a2

m1 / m2 = a2/ a1

= (m2/m1)* a2

= (4/3)*12

Hence,                    a1= 16 m/s2

Thus the acceleration of the other body is 16 m/s2.

2) A ball of mass 1 kg moving with a speed of 10 ms-1 rebounds after a perfect elastic collision with the floor. Calculate the change in linear momentum of the ball.

Ans:

Given that, mass of ball = 1kg

Velocity of ball before collision= u = 10m/s

Now, here is the ball rebounds after the perfect elastic collision, hence there is no loss of kinetic energy of the body.

Hence, velocity of the ball after collision= v = -10m/s

Thus, change in momentum= P = m (v- u)

P= 1*(-10-10)

P = -20 kgm/s

Thus, the change in momentum is P= -20 kgm/s

3) A mechanic unscrew a nut by applying a force of 140 N with a spanner of length 40 cm. What should be the length of the spanner if a force of 40 N is applied tounscrew the same nut?

Ans:

Given that, F1= 140N then L1 = 40 cm

When F2= 40N then L2=?

Here, we have to unscrew the same nut but force applied is changed.

Hence, the moment of couple required to unscrew the nut will be same although force and length of the spanner is changed.

Thus, moment of couple due to spanner first=M= F1*L1

Moment of couple due to other spanner = M =F2*L2

F1*L1 = F2*L2

L2= (F1/F2)*L1

L2 = (140/40)*40 = 140 cm

Thus, the length of the spanner should be 140 cm if the force is 40N.

4.) The ratio of masses of two planets is 2:3 and the ratio of their radii is 4:7 find the   ratio of their accelerations due to gravity.

Ans:

Given that, the ratio of masses of two planets is = M1:M2 = 2:3

Ratio of their raddi = R1:R2 = 4:7

The acceleration due to gravity is given by,

g = (GM)/R2

i.e. g α M/R2

Hence, g1αM1/R12   and g2 α M2/R22

We can write as,        g1/g2 = (M 1/M2) *(R2/R1)2

= (2/3)*(7/4)2 = (2*49)/ (3*16) = 49/24

g1/g2= 49/24

Thus, the ratio of their acceleration due to gravity is 49:24.

1) What are the types of inertia? Give an example for each type.

Ans:

Inertia is the property of a body due to which it resist the change in its state of rest or the state of motion, unless the external unbalanced force is applied on it.

The classification of inertia is as given below:

1) Inertia of rest:

It is the resistance offered by the body when we have to change state of rest of that body.

For example: the dust particles on the cloth are in the state of rest but when we shake or dusted that cloth dust particles falls down.

2) Inertia of motion:

It is the resistance offered by the body when we have to change state of motion of that body.

For example: when we are sitting in the car and car is moving with some speed that means it is in motion but when car stops by breaking then body pulls forward.

3) Inertia of direction:

It is the resistance offered by the body when we have to change the direction of motion of that body.

For example: when a car is moving on the straight road and if a turn is reached it moves or takes turn.

2) State Newton’s laws of motion?

Ans:

Newton’s first law of motion:

According to Newton’s first law of motion, everybody remains in a state of rest or the state of uniform motion along a straight line until it is acted upon by some external unbalanced force.

Newton’s second law of motion:

According to Newton’s second law of motion, the force acting on the body is directly proportional to the rate of change in linear momentum of the body and the direction of change in momentum is in the direction of force applied.

Newton’s third law of motion:

According to Newton’s third law of motion, to every action there is an equal and opposite reaction always.

2) Deduce the equation of a force using Newton’s second law of motion.

Ans:

Newton’s second law of motion:

According to Newton’s second law of motion, the force acting on the body is directly proportional to the rate of change in linear momentum of the body and the direction of change in momentum is in the direction of force applied.

Derivation for equation of force:

Let m be the mass of the body and u is the initial speed of the body.

After time t, the speed of the body will be v due to the force F acting on it.

Then, its initial momentum= P1 = m*u

And final momentum = P2 = m*v

Change in momentum= ∆P = P1 – P2

By Newton’s second law of motion,

Fα rate of change of momentum

F α change in momentum/ time

F α (mv – mu)/ t

F = km (v – u)/ t

Where k is the proportionality constant and it is 1 in all systems.

Hence,                          F = m (v-u)/ t

Since, acceleration = a = (v – u)/ t

Thus,                                    F = m*a

Force = mass * acceleration

This is the derivation for force according to Newton’s second law of motion.

3) State and prove the law of conservation of linear momentum.

Ans:

Law of conservation of linear momentum:

If there is no external force is acting on the body then its linear momentum is conserved or there is no change in momentum of the body.

Proof:

Let us consider the two bodies A and B of masses m1 and m2 are moving with initial velocity u1 and u2 along a straight line and u1>u2.

After time t, they collides with each other and both moves along the same path but with different velocities v1 and v2 respectively. Fig. Law of conservation of linear momentum

Thus, force acting on body A due to B = FB= m1* (v1 – u1) / t

And force acting on the body B due to A is = FA = m2*(v2 – u2)/t

According to Newton’s third law of motion,

Action force = reaction force

FB = – FA

m1* (v1 – u1) / t = FA = m2*(v2 – u2)/t

m1v1 + m2v2 = m1u1+m2u2

Thus, above equation shows that, when there is no external force acting on the body, the algebraic sum of momentum after collision is equal to the algebraic sum of momentum before collision that is the momentum of the body is conserved.

4) Describe rocket propulsion.

Ans:

The rocket propulsion mainly depends on the law of conservation of linear momentum and Newton’s third law of motion. In the propellant tank of the rocket, the fuel is filled. When rocket is fired this fuel starts to burn by ejecting a hot gas with high speed and huge momentum.

Now to balance this momentum, an equal and opposite reaction is produced due to which the rocket get projected in forward direction. as the fuel burnt out totally, the mass of rocket decreases. And linear momentum is conserved because there is no external force acting.

As the altitude increases the mass of the rocket decreases and thereby its speed also increases. After some time the rocket will reach to a particular altitude where it will escapes from the gravitational pull with a velocity called as escape velocity.

5) State the universal law of gravitation and derive its mathematical expression

Ans:

Newton’s Universal law of gravitation:

According to Newton’s Universal law of Gravitation, every particle of matter attracts every other particle in the universe with a force which is directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between this particles. And this force between the masses is always attractive.

Let m1 and m2 be the masses of two bodies which are separated by distance r, then according to this law,

F α m1*m2 Fig. Universal law of gravitation

Fα1/r2

Finally, F αm1*m2/ r2

F = G m1m2/ r2

Where G is the universal gravitational constant having value 6.674* 10-11 Nm2kg-2.

Above is the mathematical expression for the Newton’s Universal Law of Gravitation.

7) Give the applications of universal law gravitation.

Ans:

Following are applications of Newton’s universal law of gravitation:

• The dimensions of heavenly bodies like mass of earth, radius of earth, acceleration due to gravity etc. can be calculated accurately by using Newton’s universal law of gravitation.
• It also helps in discovering the new stars and planets.
• There is an irregularity in the motion of stars which is called as Wobble due to which the motion of nearby planet get disturbed. And in this condition also, the mass of star will be calculated by using this law of gravitation.
• Geotropism the property of roots to respond the gravity leads to germination of roots that can be also explained by law of gravitation.
• The path of the astronomical bodies can be predicted by using Newton’s Universal law of gravitation.

HOT Questions

1) Two blocks of masses 8 kg and 2 kg respectively lie on a smooth horizontal surface in contact with one other.  They are pushed by a horizontally applied force of 15 N. Calculate the force exerted on the 2 kg mass.

Ans:

Given that, the masses of two blocks are m1= 8kg and m2= 2kg

Both the blocks are in contact with each other, and force applied on both combine is F= 15N.

Thus, F= (m1 + m2)*a = (8 + 2)*a

15= 10*a

Hence, a= 3/2= 1.5 m/s2

Thus, force exerted on the block of mass 2kg by the block of mass 8kg is given by,

F1= m1*a

F1 = 8*3/2 = 12N

F1= 12N

2.) A heavy truck and bike are moving with the same kinetic energy. If the mass of the truck is four times that of the bike, then calculate the ratio of their momenta. (Ratio of momenta = 2:1)

Ans:

Let m1 be the mass of truck and m2 be the mass of bike.

And v1 be the velocity of truck and v2 be the velocity of bike.

Given that, m1=4m2

And, the truck and bike are moving with the same kinetic energy.

Hence, m1 v12= m2 v22

But, m1=4 m2

4m2 v12 = m2 v22

V1/v2 = ½

V2 = 2 v1

Thus, the ratio of their momenta would be,

P1/p2 = m1v1/ m2v2 = 4m2v1/m2v2 = 2

P1: p2 = 2:1

3) “Wearing helmet and fastening the seat belt is highly recommended for safe journey” Justify your answer using Newton’s laws of motion

Ans:

Wearing helmet and fastening the seat belt is highly recommended for safe journey in cars and bikes because, when this vehicles are in full speed our body also moves in the direction of velocity. But when some obstacles comes we stop the vehicle by applying break.

Due to which the vehicle will be stopped but our body moves forward only for some time.

And hence passengers in the vehicles get injured.

To become safe in journey wearing belt is made compulsory.

Updated: June 29, 2021 — 12:50 am