Chapter 10: FORCE AND MOTION
Chapter 10. Force and Motion Class 10 Science and Technology (212) NIOS Textbook Solutions
Chapter 10. FORCE AND MOTION
INTEXT QUESTIONS 10.1
1. Is there any force applied when a cricket player changes the direction of ball by using his/her bat?
Answer: Yes, force is applied when a cricket player changes the direction of the ball using the bat. The force exerted by the bat changes the ball’s direction of motion, showing that force can change the direction of a moving object.
2. Give an example from your daily life in which the shape of an object changes by applying a force.
Answer: An example is pressing a lump of dough with your hands. The force applied changes the shape of the dough.
INTEXT QUESTIONS 10.2
1. What are balanced forces?
Answer: When two or more forces acting on an object in opposite direction balances each other then the forces are known as balanced forces.
2. Can a balanced force produces any acceleration in a body?
Answer: No, a balanced force cannot produce acceleration in a body. Balanced forces do not change the state of motion of an object.
3. What type of change can be produced by an unbalanced force in a body?
Answer: An unbalanced force can change the state of rest or motion of a body. It may make a stationary object move or change the speed or direction of a moving object.
INTEXT QUESTIONS 10.3
1. Why does water comes out from a wet piece of cloth when you shake it?
Answer: Water comes out from a wet piece of cloth due to inertia of rest. When we shake the cloth, the water remains in its position and comes out.
2. Why do we fall forward, when a moving bus stops suddenly?
Answer: We fall forward when a moving bus stops suddenly due to inertia of motion. When the bus stops, our feet stop with the bus, but the upper part of the body continues moving forward, causing us to fall forward.
3. Two similar trucks are moving on a road with the same velocity. One of them is empty while the other one is loaded. Which of the two has more momentum?
Answer: Momentum = mass × velocity. Since both trucks have the same velocity, the loaded truck has more mass. Therefore, the loaded truck has more momentum.
4. If a body of mass 5 kg moves with a velocity of 10 m/s, then what is the momentum of the body?
Answer: Here, m = 5 kg and v = 10 m/s
We have, Momentum = Mass × Velocity =mv 
= 5 kg × 10 m/s
= 50 kg m/s
Therefore, the momentum of the body is 50 kg m/s.
5. Why does a boxer move his head backward while taking an oncoming punch?
Answer: A boxer moves his head backward while taking an oncoming punch to increase the time of impact. This reduces the force of the punch and helps prevent injury.
INTEXT QUESTIONS 10.4
1. Why does a fast moving car slow down when its engine is switched off?
Answer: A fast moving car slows down when its engine is switched off due to the force of friction acting between the wheels of the car and the ground.
2. Why do we slip when we step on a banana peel?
Answer: We slip when we step on a banana peel because the friction between the banana peel and the ground is very small. This low friction makes it difficult to maintain balance.
3. Why are tyres of automobiles treaded?
Answer: Tyres of automobiles are treaded to provide better grip with the ground because treaded tyres increase friction between the tyres and the ground. This helps prevent slipping.
INTEXT QUESTIONS 10.5
1. Why does a porter carrying a heavy load place a round piece of cloth on his head?
Answer: A porter carrying a heavy load places a round piece of cloth on his head because it increases the area of contact between the load and the head, thereby decreasing the pressure on his head.
2. Why a nail has a pointed tip?
Answer: A nail has a pointed tip because the pointed end has a smaller area of contact, which increases pressure. This helps the nail penetrate easily into wood or other materials.
3. Why shoulder bags are provided with broad straps?
Answer: Shoulder bags are provided with broad straps because they increase the area of contact on the shoulder, thereby reducing pressure and making the bag more comfortable to carry.
4. State the SI unit of pressure.
Answer: The SI unit of pressure is N/m² or pascal (Pa).
TERMINAL EXERCISE
1. Why does a sprinter keep running for sometime even after crossing the finish line?
Answer: A sprinter keeps running for some time even after crossing the finish line due to inertia of motion. The body continues to remain in motion and cannot stop suddenly.
2. Why is it advised to tie the luggage with a rope on the roof of busses?
Answer: It is advised to tie the luggage with a rope on the roof of buses because due to inertia, the luggage may continue in its state of rest or motion and fall off during sudden starts, stops, or turns.
3. Why do the dust particles from the hanging blanket fall off when it is beaten with a stick?
Answer: The dust particles fall off from a hanging blanket when it is beaten with a stick due to inertia of rest. The blanket moves suddenly, but the dust particles remain at rest and get separated.
4. State Newton’s first law of motion. Why do the passengers standing in a stationary bus fall in the backward direction when the bus begins to move suddenly.
Answer: Newton’s first law of motion states that, everybody continues in its state of rest or of uniform motion in a straight line until unless it is compelled by some unbalanced force to change that state.
Passengers standing in a stationary bus fall backward when the bus begins to move suddenly due to inertia of rest. Their feet move with the bus, but the upper part of the body tends to remain at rest, causing them to fall backward.
5. Define momentum. How the rate of change of momentum is related to force?
Answer: The momentum of a body is the product of its mass and velocity. The SI unit of momentum is kg m/s.
The rate of change of momentum of a body is directly proportional to the applied force and takes place in the direction of the force.
6. If a body of mass 10 kg moves with a velocity of 7 m/s , then what is the momentum of the body?
Answer: Given, m=10kg and v=7m/s
We have, Momentum = mass × velocity
i.e., p=mv 
p=10 kg×7 m/s=70 kg⋅m/s
Therefore, the momentum of the body is 70 kg·m/s.
7. If a force of 50 N acts on a body of mass 10 kg then what is the acceleration produced in the body?
Answer: Here, F=50 N 
, m=10 kg 
and a= ? 
We have,
F=ma 
⇒a=Fm=5010 
⇒a=5 
m/s²
Therefore, the acceleration produced in the body is 5 m/s².
8. State Newton’s third law of motion. Why it is difficult for a fireman to hold a hose pipe which ejects larger amount of water at a high speed?
Answer: Newton’s third law of motion states that, to every action there is always an equal and opposite reaction. Action and reaction always act on two different bodies.
It is difficult for a fireman to hold a hose pipe ejecting a large amount of water at high speed because the water coming out exerts an equal and opposite reaction force on the hose pipe, pushing it backward.
9. “Action and reaction forces are equal in magnitude and opposite in direction”. Then, why do they not balance each other?
Answer: Action and reaction forces do not balance each other because they act on two different bodies. Balanced forces must act on the same body, whereas action and reaction act on separate bodies.
10. A motorcycle is moving with a velocity of 72 km/h and it takes 6 s to stop after the breaks are applied. Calculate the force exerted by the breaks on the motorcycle, if its mass along with the rider is 175 kg.
Answer: Given, m = 175 kg , 
, v = 0 m/s and t = 6 s
We have, 
Using Newton’s second law:
F=ma 
F =175×-3.33=-582.75 N 
Therefore, the force exerted by the brakes on the motorcycle is 582.75 N opposite to the direction of motion.
11. An object of mass 2 kg travelling in a straight line with a velocity of 10 m/s collides with and sticks to a stationary object of mass 6 kg. Then they both move off together in the same straight line. Calculate the total momentum just before the impact and just after the impact.
Answer: Given, Mass of first object (m₁) = 2 kg
Velocity of first object (v₁) = 10 m/s
Mass of second object (m₂) = 6 kg
Velocity of second object (v₂) = 0 m/s
Total momentum before impact:
p=m1v1+m2v2 
p=2×10+6×0=20 kg m/s 
So, the total momentum just before the impact is 20 kg m/s.
According to the law of conservation of momentum, when no external force acts, the total momentum before the collision equals the total momentum after the collision.
pafter=pbefore=20 kg m/s 
Total momentum after impact = 20 kg m/s.
12. What is the force of friction? State two methods to reduce friction.
Answer: Force of friction is the opposing force that acts when one object moves or tries to move over the surface of another object. It always acts in the opposite direction to the motion.
Two methods to reduce friction:
(i) By applying lubricants like oil or grease.
(ii) By using rollers or ball bearings.
13. What is the relation between thrust and pressure? State the SI units of thrust and pressure. Why a camel can run in a desert easily?
Answer: The relation between thrust and pressure is
Pressure=ThrustArea 
SI unit of thrust: Newton (N) and SI unit of pressure: Pascal (Pa) or N/m² .
A camel can run easily in a desert because its broad feet have a larger area of contact with the sand, which reduces pressure and prevents it from sinking.
14. A block of wood kept on a table applies a thrust of 49 N on the table top. The dimensions of the wooden block are 40 cm × 20 cm × 10 cm. Calculate the pressure exerted by the wooden block if it is made to lie on the table top with its sides of dimensions (a) 20 cm × 10 cm and (b) 40 cm × 20 cm.
Answer: Given, F = 49N
We know that,
Pressure=ThrustArea
(a) Here, Area
=20 cm×10 cm=20100×10100 m²=0.2×0.1 m²=0.02 m² 
Pressure
=49 N0.02 m²=2450 N/m²=2450 Pa 
Therefore, the pressure = 2450 Pa (or 2450 N/m²)
(b) Here, Area 
Pressure=49 N0.08 m²=612.5 N/m² 
Therefore, the pressure = 612.5 Pa (or 612.5 N/m²)
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