1. Match the first column with appropriate entries in the second and third columns and remake the table.

S.NO.	Column 1	Column 2	Column 3
1	Negative acceleration	e velocity of an object decreases	A car moving with 20 m/s stops after 10 seconds
2	Positive acceleration	The velocity of an object increases	Acar initially at rest reaches a velocity 50 km/hr in 10 seconds
3	Zero acceleration	e velocity of an object remains constant	A bus moving with the speed of 30 m/s

 

2. Clarify the differences

A. Distance and  Displacement

Distance	Displacement
Distance is the total length of the path traveled by an object, regardless of its direction.	Displacement is the shortest distance between the object’s starting and ending points, taking into account the direction of its motion.
Distance is a scalar quantity, which means it only has magnitude.	Displacement is a vector quantity, which means it has both magnitude and direction.
Distance traveled is always positive	e distance traveled by an object can be greater than, equal to, or less than its displacement

 

B. Uniform and non-uniform motion.
Answer:

Uniform Motion	Nonuniform motion
Uniform motion is a type of motion in which an object travels at a constant speed in a straight line. This means that the object covers equal distances in equal time intervals.	Non-uniform motion is a type of motion in which an object’s speed or direction of motion changes. This means that the object does not cover equal distances in equal time intervals.
The velocity of an object in uniform motion is constant. This means that the object’s speed and direction of motion do not change.	The velocity of an object in non-uniform motion is not constant. This means that the object’s speed and direction of motion may change.
Examples of uniform motion include A car driving at a constant speed on a straight highway.	Examples of non-uniform motion are a car accelerating or decelerating. A train slows down as it approaches a station.

 

3. Complete the following table.

 

u(m/s)	a (m/s2)	t(sec)	v=u+at(m/s)
2	4	3	14
10	5	2	20
u(m/s)	a (m/s2)	t(sec)	S=ut +1/2 at2 (m)
5	12	3	69
7	8	4	92
u(m/s)	a (m/s2)	s(m)	V2=u2 +2as(m/s2)
4	3	8	8
4	5	8.4	10

4. Complete the sentences and explain them.

a. The minimum distance between the start and finish points of the motion of an object is called the

displacement    of the object.
b. Deceleration is Negative  acceleration
c. When an object is in a uniform circular motion, its velocity changes at every point.
d. During collision momentum of the system remains constant.
e. The working of a rocket depends on Newton’s third  law of motion

5. Give scientific reasons.

A. When an object falls freely to the ground, its acceleration is uniform.

• When a body falls freely to the ground, its velocity increases by an equal amount in equal intervals of time.
• This means that the acceleration of the body is constant.
• The acceleration of a freely falling body is equal to the acceleration due to gravity, which is approximately 9.8 m/s².

B. Even though the magnitudes of action force and reaction forces are equal and their directions are opposite, their effects do not get canceled.

Answer. The action force and reaction forces do not cancel each other out because they act on different objects. The action force is the force that one object exerts on another object, and the reaction force is the force that the second object exerts on the first object. These two forces are always equal in magnitude and opposite in direction, but they act on different objects, so they cannot cancel each other out.

For example, when you jump, you exert a force on the ground (the action force). The ground exerts an equal and opposite force on your feet (the reaction force). These two forces do not cancel each other out because they act on different objects: the action force acts on the ground, and the reaction force acts on your feet.

The action and reaction forces are an important part of Newton’s third law of motion, which states that there is an equal and opposite reaction for every action. This law is responsible for many of the forces that we experience in everyday life, such as the force of gravity, the force of friction, and the force of thrust.

C. It is easier to stop a tennis ball as compared to a cricket ball when both are traveling with the same velocity.

Answer. It is easier to stop a tennis ball than a cricket ball when both are traveling with the same velocity because the tennis ball has less momentum. Momentum is the product of mass and velocity, so a lighter object with the same velocity will have less momentum than a heavier object.

The force required to stop an object is equal to its momentum divided by the time it takes to stop. So, if a tennis ball has less momentum than a cricket ball, it will require less force to stop.

All of these factors contribute to making it easier to stop a tennis ball than a cricket ball when both are traveling at the same velocity.

The velocity of an object at rest is considered to be uniform.

The velocity of an object at rest is considered to be uniform because the object is not moving. An object at rest has a speed of zero, and its direction of motion does not change. Therefore, its velocity is constant, or uniform.

In physics, the term “uniform” means that something does not change. So, when we say that the velocity of an object at rest is uniform, we mean that its speed and direction of motion do not change.

This may seem counterintuitive since we usually think of “uniform” as meaning “constant speed.” However, in physics, “uniform” can also mean “constant direction of motion.” And since an object at rest is not moving, its direction of motion does not change.

So, while the velocity of an object at rest may not seem to be “uniform” in the traditional sense, it is indeed uniform in the sense that its speed and direction of motion do not change.

d. The velocity of an object at rest is considered to be uniform.

Answer. The velocity of an object at rest is considered to be uniform because the object is not moving. An object at rest has a speed of zero, and its direction of motion does not change. Therefore, its velocity is constant, or uniform.

In physics, the term “uniform” means that something does not change. So, when we say that the velocity of an object at rest is uniform, we mean that its speed and direction of motion do not change.

This may seem not easy to understand since we usually think of “uniform” as meaning “constant speed.” However, in physics, “uniform” can also mean “constant direction of motion.” And since an object at rest is not moving, its direction of motion does not change.

So, while the velocity of an object at rest may not seem to be “uniform” in the traditional sense, it is indeed uniform in the sense that its speed and direction of motion do not change.

6. Take 5 examples from your surroundings and give an explanation based on Newton’s laws of motion.

1. A car coming to a stop. This is an example of Newton’s first law of motion, also known as the law of inertia. The car is moving at a constant speed until the brakes are applied. The brakes apply a force to the car, which slows it down and eventually brings it to a stop.
2. A tennis ball bouncing off a wall. This is an example of Newton’s third law of motion, also known as the law of action and reaction. When the tennis ball hits the wall, it exerts a force on the wall. The wall exerts an equal and opposite force on the tennis ball, which causes it to bounce back.
3. A rocket taking off. This is an example of Newton’s third law of motion. The rocket engine exerts a force on the exhaust gases, which are expelled out the back of the rocket. The exhaust gases exert an equal and opposite force on the rocket, which propels it forward.
4. A person walking. This is an example of Newton’s third law of motion. When a person walks, they push against the ground with their feet. The ground exerts an equal and opposite force on the person, which propels them forward.
5. A bicycle slows down when you apply the brakes. This is an example of Newton’s first law of motion. When you apply the brakes, you are applying a force to the bicycle. This force slows down the bicycle and eventually brings it to a stop.

7. Solve the following examples.

(a) An object moves 18 m in the first 3 s, 22 m in the next 3 s, and 14 m in the last 3 s. What is its average speed? (Ans: 6 m/s)

Answer. The average speed of an object is the total distance traveled divided by the total time taken. In this case, the total distance traveled is 18 + 22 + 14 = 54 m. The total time taken is 3 + 3 + 3 = 9 s. Therefore, the average speed is 54/9 = 6 m/s.

Here is a more detailed explanation of the solution:

• In the first 3 s, the object travels 18 m. This means that its average speed in the first 3 s is 18/3 = 6 m/s.
• In the next 3 s, the object travels 22 m. This means that its average speed in the next 3 s is 22/3 = 7.33 m/s.
• In the last 3 s, the object travels 14 m. This means that its average speed in the last 3 s is 14/3 = 4.67 m/s.
• The average speed of the object is calculated by taking the average of its average speeds in three-time intervals. So, the average speed is (6 + 7.33 + 4.67)/3 = 6 m/s.

 

(b) An object of mass 16 kg is moving with an acceleration of 3 m/s². Calculate the applied force. If the same force is applied to an object of mass 24 kg, how much will be the acceleration? (Ans: 48 N, 2 m/s²)

Answer. The force applied to an object is equal to its mass times its acceleration. So, the force applied to the object of mass 16 kg is 16 kg x 3 m/s² = 48 N.

If the same force is applied to an object of mass 24 kg, the acceleration will be 48 N / 24 kg = 2 m/s².

Here is a more detailed explanation of the solution:

• Force: Force is the interaction between two objects that causes them to accelerate. It is measured in Newtons (N).
• Mass: Mass is the amount of matter in an object. It is measured in kilograms (kg).
• Acceleration: Acceleration is the rate of change of velocity. It is measured in meters per second squared (m/s²).

In this case, we know that the mass of the object is 16 kg and the acceleration is 3 m/s². We can use the following equation to calculate the force:

Force = Mass x Acceleration

Force = 16 kg x 3 m/s² = 48 N

This means that a force of 48 N is needed to accelerate the object of mass 16 kg to an acceleration of 3 m/s².

We can also use the same equation to calculate the acceleration of the object if the same force is applied to an object of mass 24 kg.

Acceleration = Force / Mass

Acceleration = 48 N / 24 kg = 2 m/s²

This means that the acceleration of the object of mass 24 kg will be 2 m/s² if the same force of 48 N is applied.

(c) A bullet having a mass of 10 g and moving with a speed of 1.5 m/s, penetrates a thick wooden plank of mass 90 g. The plank was initially at rest. The bullet gets embedded in the plank and both move together. Determine their velocity. (Ans: 0.15 m/s)
Answer: The law of conservation of momentum states that the total momentum of a system remains constant. Momentum is mass times velocity.

Let the mass of the bullet be m = 10 g Let the velocity of the bullet be v = 1.5 m/s Let the mass of the plank be M = 90 g Let the velocity of the bullet and the plank after the collision be ve

The total momentum of the system before the collision is:

m x v

The total momentum of the system after the collision is:

(m + M) x v’

Since the momentum is conserved, we can equate the momentum of the system before and after the collision.

m x v = (m + M) x v’v’ = m * v / (m + M)v’ = (10 g) x (1.5 m/s) / (10 g + 90 g) v’ = 0.15 m/s

Therefore, the velocity of the bullet and the plank after the collision is 0.15 m/s.

d)A person swims 100 m in the first 40 s, 80 m in the next 40 s, and 45 m in the last 20 s. What is the average speed? (Ans: 2.25 m/s²)

The average speed is calculated by dividing the total distance traveled by the total time taken. In this case, the total distance traveled is 100 m + 80 m + 45 m = 225 m. The total time taken is 40 s + 40 s + 20 s = 100 s.

Therefore, the average speed is:

average speed = total distance / total time= 225 m / 100 s= 2.25 m/s