Questions Related to NCERT

When an object moves with constant velocity, the applied force is balanced by the friction force.
So, the friction force = applied force = 200 N

(d) mv
Momentum is the product of mass and velocity.
Formula: momentum (p) = m × v

Mass (m) = 1500 kg
Acceleration (a) = –1.7 m/s² 

Use the formula:
Force (F) = mass × acceleration
F = 1500 × (–1.7)
F = –2550 N

Hence the force between the vehicle and the road must be 2550 N opposite to the direction of motion.

Given:
Mass of engine = 8000 kg
Mass of each wagon = 2000 kg
Number of wagons = 5
Total mass of wagons = 5 × 2000 = 10000 kg
Total mass of train = 8000 + 10000 = 18000 kg
Force by engine = 40000 N
Friction force = 5000 N

(a) Net accelerating force = Force by engine − Friction force
Net force = 40000 − 5000 = 35000 N

(b) Acceleration of the train = Net force ÷ Total mass
a = 35000 ÷ 18000 = 1.94 m/s² (approximately)

Hence:-
(a) Net accelerating force = 35000 N
(b) Acceleration of the train = 1.94 m/s²

Mass (m) = 1 kg
Initial velocity (u) = 20 m/s
Final velocity (v) = 0 m/s (comes to rest)
Distance (s) = 50 m

Step 1: Find acceleration (a)
Use the formula:
v² = u² + 2as
=> 0 = (20)² + 2 × a × 50
=> 0 = 400 + 100a
=> 100a = -400
=> a = -400 ÷ 100 = -4 m/s²

Step 2: Find the force (F)
Use the formula:
F = m × a
F = 1 × (-4) = -4 N

Hence force of friction = 4 N (opposite to direction of motion)

initial velocity (u) = 0 m/s
Distance (s) = 400 m
Time (t) = 20 s
Mass (m) = 7 tonnes = 7000 kg

Step 1: Find acceleration (a)
Use the formula:
s = ut + (1/2)at²
=> 400 = 0 × 20 + (1/2) × a × (20)²
=> 400 = (1/2) × a × 400
=> 400 = 200a
=> a = 400 ÷ 200 = 2 m/s²

Step 2: Find the force (F)
Use the formula:
F = m × a
F = 7000 × 2 = 14000 N

Hence  Acceleration = 2 m/s²  &  Force = 14000 N

(c) there is a force on the ball opposing the motion.

Explanation:  The ball comes to rest because of friction between the ball and the ground. This frictional force opposes the motion of the ball and slows it down until it stops.

When a carpet is beaten with a stick, the carpet moves suddenly, but the dust particles tend to stay in their original position due to inertia. Because of this, the dust gets separated from the carpet and comes out.

This happens due to Newton’s First Law of Motion, which says that an object at rest will stay at rest unless an external force acts on it. The dust remains at rest while the carpet moves, so it gets left behind.

It is advised to tie the luggage on the roof of a bus with a rope to stop it from falling off when the bus moves suddenly, stops, or turns.
Because of inertia, the luggage tries to stay in the same position.

1. If the bus starts quickly, the luggage may fall backward.
2. If the bus stops suddenly, the luggage may fall forward.
3. If the bus turns, the luggage may slide to the side.

Yes, it is possible for the object to travel with a non-zero velocity even when the net external unbalanced force is zero.

Condition:
The object must be moving with a constant speed in a straight line. This means its velocity should not change.
According to Newton's First Law of Motion, an object will keep moving with the same velocity unless an unbalanced force acts on it. So, if the net force is zero, the object can keep moving at a steady speed.

When a moving bus stops suddenly, your body keeps moving forward due to inertia, so you fall forward. When the bus starts moving from rest, your body tries to stay in the same place due to inertia, so you fall backward.
Inertia is the tendency of the body to resist any change in its state of rest or motion.

When we vigorously shake the branch of a tree, the branch moves suddenly, but the leaves tend to stay in their original position due to inertia. Inertia is the tendency of an object to resist any change in its state of rest or motion.

As a result, the leaves cannot follow the motion of the branch and may get detached. This is explained by Newton’s First Law of Motion, which states that an object at rest stays at rest unless acted upon by an external force.

The velocity of the ball changes three times.

1. First player kicks the football to another player – velocity changes
2. Second player kicks it towards the goal – velocity changes again
3. Goalkeeper kicks it towards his teammate – velocity changes once more

So, velocity changes 3 times.

(a) A rubber ball and a stone of the same size

        Answer: The stone has more inertia.
        Reason: Inertia depends on mass. Since the stone is heavier than the rubber ball, it has more inertia.

(b) A bicycle and a train

        Answer: The train has more inertia.
        Reason: The train has much more mass than the bicycle, so it resists changes in motion more and has more inertia.

(c) A five-rupees coin and a one-rupee coin

        Answer: The five-rupees coin has more inertia.
        Reason: It has more mass than the one-rupee coin, so it has greater inertia.

Difference between movement in a sensitive plant and movement in our legs:

Movement in a sensitive plant (like Mimosa pudica):

1. This movement happens in response to touch (a stimulus).
2. It is a nastic movement (non-directional).
3. It does not involve muscles.
4. It is caused by changes in water pressure in plant cells.
5. It does not involve the brain or nerves.

Movement in our legs:

1. This is a voluntary movement, controlled by our brain.
2. It happens due to muscle contraction and relaxation.
3. It involves the nervous system and muscular system.
4. The movement is purposeful and directional.

The nervous system uses electrical impulses to send messages through nerves. It works very fast and controls actions like movement or reflexes. The response is usually short-term and controlled by the brain and spinal cord. For example, pulling your hand away from a hot object is controlled by the nervous system.

The hormonal system (also called the endocrine system) uses chemical messengers called hormones. These hormones are released by endocrine glands into the bloodstream and work slowly. The effects are usually long-lasting and can affect multiple organs. For example, insulin controls the sugar level in the blood.

Difference between Involuntary Actions and Reflex Actions:

Involuntary Actions:

1. These are actions that happen automatically without our control.
2. Controlled by the brain.
3. Example: Beating of the heart, breathing, digestion.
4. They are slow and continuous.

Reflex Actions:

1. These are quick and automatic responses to a stimulus.
2. Controlled by the spinal cord.
3. Example: Pulling hand away from a hot object.
4. They are sudden and protective.

All organisms need a system of control and coordination to:

1. Respond to changes in their surroundings (like light, sound, touch, temperature).
2. Carry out body functions in an organized way (like movement, digestion, breathing).
3. Maintain balance between different parts of the body.
4. Protect the body from harm through quick responses (like reflex actions).

Chemical coordination in plants takes place with the help of plant hormones (also called phytohormones). These hormones are chemical messengers that control and coordinate various activities like growth, development, and responses to the environment.

Different hormones have different functions, such as:

1. Auxins – help in growth of stem and bending towards light
2. Gibberellins – help in seed germination and growth
3. Cytokinins – help in cell division
4. Abscisic acid – controls falling of leaves and closing of stomata
5. Ethylene – helps in ripening of fruits

In case of a spinal cord injury, the signals between the brain and the rest of the body will get disrupted. This includes:

1. Sensory signals(from body to brain) – such as touch, pain, and temperature.
2. Motor signals(from brain to body) – that control muscle movement and reflexes.