Chapter 2 Solution: FORCE AND LAWS OF MOTION Class 9
Very Short Answer Type Questions
1. What name is given to the product of mass and velocity of a body?
Answer: Momentum
2. Name the physical quantity which is considered to be a measure of the quantity of motion of a body.
Answer: Momentum
3. What is the SI unit of momentum?
Answer: The SI unit of momentum is kilogram meter per second (kg.m/s).
4. State whether momentum is scalar or vector.
Answer: Momentum is a vector quantity.
5. What is the total momentum of the bullet and the gun before firing?
Answer: The total momentum before firing is zero (assuming no external forces act).
6. Name the physical quantity whose unit is kg.m/s.
Answer: Momentum
7. What will be the momentum of a body of mass ‘m’ which is moving with a velocity ‘v’?
Answer: Momentum (p) = m * v
8. What is the usual name of the forces which cannot produce motion in a body but only change its shape?
Answer: Balanced forces
9. Name the unbalanced force which slows down a moving bicycle when we stop pedaling.
Answer: Friction
10. State whether the following statement is true or false:
Unbalanced forces acting on a body change its shape.
Answer: False
11. When a ball is dropped from a height, its speed increases gradually. Name the force which causes this change in speed.
Answer: Gravity
12. Name the property of bodies (or objects) to resist a change in their state of rest or of motion.
Answer: Inertia
13. What is the other name of Newton’s first law of motion?
Answer: The Law of Inertia or Galileo’s law of inertia
14. The mass of object A is 6 kg whereas that of another object B is 34 kg. Which of the two objects, A or B, has more inertia?
Answer: Object B has more inertia.
15. Name the scientist who gave the laws of motion.
Answer: Sir Isaac Newton
16. State whether force is a scalar or a vector quantity.
Answer: Force is a vector quantity.
17. With which physical quantity should the speed of a running bull be multiplied so as to obtain its momentum?
Answer: Mass (momentum = mass * velocity)
18. Fill in the following blanks with suitable words:
(a) **Mass** is a measure of the inertia of a body.
(b) When a running car stops suddenly, the passengers are jerked **forward**.
(c) When a stationary car starts suddenly, the passengers are jerked **backward**.
(d) Newton’s first law of motion is also called Galileo’s law of **inertia**.
(e) If there were no unbalanced force of **friction** and no **air resistance**, a moving bicycle would go on moving forever.
Short Answer Type Questions
19. Explain why, it is easier to stop a tennis ball than a cricket ball moving with the same speed.
Answer: The tennis ball is easier to stop than a cricket ball due to its lower mass, resulting in lower momentum, according to the momentum equation
p=m×v.
20. Explain the meaning of the following equation :
p = m × v
Answer: The equation p=m×v defines momentum (p) as the product of mass (m) and velocity (v).
where symbols have their usual meanings.
21. Explain how, a karate player can break a pile of tiles with a single blow of his hand.
Answer: A karate player breaks tiles with a single hand blow by concentrating force over a small area, increasing pressure enough to overcome the tiles' resistance.
22. Calculate the momentum of a toy car of mass 200 g moving with a speed of 5 m/s.
Answer: Momentum (p) of the toy car = m×v = 0.2 kg×5 m/s=1 kg.m/s
23. What is the change in momentum of a car weighing 1500 kg when its speed increases from 36 km/h to
72 km/h uniformly ?
Answer:
The change in momentum (Δp) is calculated using the formula:
Δp=m×Δv
where m is the mass of the object and Δv is the change in velocity.
Given:
- Mass (m) of the car = 1500 kg
- Initial speed = 36 km/h
- Final speed = 72 km/h
First, we need to convert the speeds from km/h to m/s because the SI unit for velocity is meters per second (1 m/s=3.6 km/h1m/s=3.6km/h).
Initial velocity =36 km/h/3.6=10 m/s
Final velocity =72 km/h/3.6=20 m/s
Now, calculate the change in velocity (Δv):
Final velocity - Initial velocity = 20m/s−10m/s=10m/s
Finally, calculate the change in momentum (Δp):
=m×Δv=1500 kg×10 m/s=15000 kg.m/s
So, the change in momentum of the car is 15000 kg.m/s1. when its speed increases from 36 km/h to 72 km/h7 uniformly.
24. A body of mass 25 kg has a momentum of 125 kg.m/s. Calculate the velocity of the body.
Answer: Velocity (v) of the body = p/m= 125kg.m/s/25kg=5m/s.
25. Calculate the momentum of the following :
(a) an elephant of mass 2000 kg moving at 5 m/s
(b) a bullet of mass 0.02 kg moving at 400 m/s
(a) Answer: Momentum (p) of the elephant = m×v = 2000 kg×5 m/s=10000 kg.m/s
(b) Answer: Momentum (p) of the bullet = m×v = 0.02 kg×400 m/s=8 kg.m/s
26. Which of the two, balanced forces or unbalanced forces, can change the shape of an object ? Give an example
to illustrate your answer.
Answer: Unbalanced forces can change the shape of an object. For instance, when a person pushes or pulls on an object with unequal forces, the object experiences deformation or changes in shape.
27. Describe the term ‘inertia’ with respect to motion.
Answer: Inertia, in the context of motion, refers to the inherent property of an object to resist changes in its state of motion. Objects with greater mass exhibit greater inertia, making them more resistant to changes in velocity. This means that an object at rest tends to stay at rest, and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an external force. Inertia is a fundamental concept in Newton's First Law of Motion, highlighting the tendency of objects to maintain their current state of motion.
28. State Newton’s first law of motion. Give two examples to illustrate Newton’s first law of motion.
Answer:
Newton's First Law of Motion: An object at rest will remain at rest, and an object in motion will remain in motion with a constant velocity unless acted upon by a net external force.
Examples:
At Rest: A book sitting on a table will stay stationary until an external force, like someone pushing it, overcomes its inertia and sets it in motion.
In Motion: A ball rolling on a frictionless surface will continue to roll at a constant speed in a straight line unless an external force, such as friction or someone pushing it, influences its motion.
29. On what factor does the inertia of a body depend ? Which has more inertia, a cricket ball or a rubber ball of
the same size ?
Answer: The inertia of a body depends on its mass.
Comparing a cricket ball and a rubber ball of the same size, the cricket ball has more inertia because it typically has a greater mass. Inertia is directly proportional to mass, so an object with a higher mass will exhibit greater resistance to changes in its state of motion.
30. Why do the passengers in a bus tend to fall backward when it starts suddenly ?
Answer: When a bus starts suddenly, the passengers inside experience a backward-leaning motion due to the principle of inertia. According to Newton's First Law of Motion, an object at rest (or in this case, the passengers) will tend to stay at rest unless acted upon by an external force.
As the bus accelerates forward, the lower part of the passengers' bodies, in contact with the bus, starts moving with it. However, the upper part of their bodies initially tends to stay at rest due to inertia. This creates a relative backward motion, causing the sensation that the passengers are falling backward. Once the passengers catch up with the bus's forward motion, they regain an upright position.
31. Explain why, a person travelling in a bus falls forward when the bus stops suddenly.
Answer:
When a bus stops suddenly, the person inside it tends to fall forward due to the principle of inertia, as described by Newton's First Law of Motion. According to this law, an object in motion will remain in motion unless acted upon by an external force.
As the bus decelerates rapidly, the lower part of the person's body, in contact with the bus, tends to continue moving forward with the bus. However, the upper part of their body, due to inertia, resists the sudden deceleration and wants to stay in motion. This creates a relative forward motion, causing the person to lean or fall forward within the bus until their body comes to rest, aligning with the new motionless state of the bus.
32. Give reason for the following :
When a hanging carpet is beaten with a stick, the dust particles start coming out of it.
Answer: When a hanging carpet is beaten with a stick, the dust particles start coming out due to the application of mechanical energy. The impact and vibration caused by the beating action transfer energy to the carpet fibers. This energy is then transmitted to the dust particles trapped within the carpet.
The mechanical energy disrupts the equilibrium of the dust particles, overcoming any forces that might have kept them attached to the carpet fibers. As a result, the dust particles are dislodged and become airborne, creating the appearance of dust coming out of the carpet. This phenomenon is a demonstration of the transfer of kinetic energy from the stick to the carpet, leading to the liberation of dust particles.
33. When a tree is shaken, its fruits and leaves fall down. Why ?
Answer: When a tree is shaken, its fruits and leaves fall down due to the force applied to the tree's branches and foliage. This force causes a disturbance in the equilibrium of the fruits and leaves.
The falling is primarily attributed to the influence of gravity and the detachment of the fruits and leaves from their attachment points. As the tree is shaken, the branches and leaves experience an external force that can overcome the forces holding the fruits and leaves in place, such as stem strength or friction between the fruits/leaves and the branches.
Additionally, the shaking motion imparts kinetic energy to the fruits and leaves, contributing to their separation from the tree. The combination of these factors results in the cascading effect of fruits and leaves falling when the tree is shaken.
34. Explain why, it is dangerous to jump out of a moving bus.
Answer:
Jumping out of a moving bus is perilous due to inertia and the physics of motion. Newton's First Law dictates that the person retains the bus's forward velocity upon jumping. This poses risks, including:
- Forward Momentum: Difficulty in landing safely and maintaining balance.
- Impact and Friction: Potential for injuries upon landing due to impact and friction with the road.
- Uneven Surfaces: Risk of encountering obstacles or irregularities in the terrain.
- Absence of Control: Limited control over trajectory and landing conditions.
Exiting a moving bus through proper exits when it stops is crucial to avoid serious injuries.
35. What is the momentum in kg.m/s of a 10 kg car travelling at (a) 5 m/s (b) 20 cm/s, and (c) 36 km/h ?
Answer:
The momentum (p) of an object is calculated using the formula p=m×v, where m is the mass in kilograms and v is the velocity in meters per second.
(a) Velocity v1 = 5 m/s:
The momentum (p1) is 50 kg.m/s.
(b) Velocity v2 = 20 cm/s:
The momentum (p2) is 2 kg.m/s.
(c) Velocity v3 = 36 km/h:
The momentum (p3) is 100 kg.m/s.
Long Answer Type Questions
36. (a) Define momentum of a body. On what factors does the momentum of a body depend ?
(b) Calculate the change in momentum of a body weighing 5 kg when its velocity decreases from 20 m/s to
0.20 m/s.
Answer:
(a) Definition and factors affecting momentum of a body:
Momentum is a physical quantity that describes the motion of an object. It is a measure of how much "mass in motion" an object has. It depends on two factors:
- Mass (m) of the object: The more massive the object, the greater its momentum for the same velocity.
- Velocity (v) of the object: The higher the velocity of the object, the greater its momentum for the same mass.
Mathematically, momentum is calculated as follows:
p = mv
where:
- p is the momentum (measured in kg m/s)
- m is the mass of the object (measured in kg)
- v is the velocity of the object (measured in m/s)
Since both mass and velocity are vector quantities, momentum is also a vector quantity. This means it has both magnitude and direction. The direction of the momentum is the same as the direction of the object's velocity.
(b) Calculating the change in momentum:
Given:
- Mass of the body (m) = 5 kg
- Initial velocity (v1) = 20 m/s
- Final velocity (v2) = 0.20 m/s
We need to find the change in momentum (Δp):
Δp = p2 - p1
where:
- p2 is the final momentum
- p1 is the initial momentum
Calculate p1 and p2:
p1 = m * v1 = 5 kg * 20 m/s = 100 kg m/s p2 = m * v2 = 5 kg * 0.20 m/s = 1 kg m/s
Calculate Δp:
Δp = p2 - p1 = 1 kg m/s - 100 kg m/s = -99 kg m/s
Therefore, the change in momentum of the body is -99 kg m/s.
37. (a) Define the term ‘force’.
(b) State the various effects of force.
Answer:
(a) Definition of Force
Force is a physical quantity that can change the state of motion of an object. It is a push or pull that acts on an object and can cause it to:
- Start moving from rest
- Stop moving
- Change its direction of motion
- Change its speed
- Deform or break
Forces are often described as vectors, meaning they have both magnitude (strength) and direction. The direction of a force is the direction in which it acts on an object.
Here are some examples of forces:
- Gravity: The force that pulls objects towards the Earth.
- Friction: The force that resists the motion of two surfaces in contact.
- Tension: The force that pulls on a rope or string.
- Compression: The force that pushes on an object, causing it to deform.
- Normal force: The force that supports an object resting on a surface.
(b) Effects of Force
A force can have various effects on an object, depending on the magnitude and direction of the force, as well as the properties of the object itself. Here are some of the common effects of force:
1. Change in state of motion:
- A force can bring an object at rest into motion.
- A force can stop a moving object.
- A force can change the speed of a moving object.
- A force can change the direction of a moving object.
2. Change in shape:
- A force can deform an object.
- A force can break an object.
3. Change in size:
- A force can stretch an object.
- A force can compress an object.
4. Generation of sound:
- When a force is applied to an object, it can vibrate. This vibration can be transmitted through the air as sound waves.
Examples of forces and their effects:
(a) Force moves a stationary body:
- Example: When you kick a stationary football, the force of your foot applies to the ball, causing it to start moving.
(b) Force stops a moving body:
- Example: When you apply the brakes of a moving car, the frictional force between the tires and the road acts to slow down and eventually stop the car.
(c) Force changes the speed of a moving body:
- Example: When you push a swing, the force of your push increases the speed of the swing.
(d) Force changes the direction of a moving body:
- Example: When a tennis player hits a ball, the force of the racket changes the direction of the ball's trajectory.
(e) Force changes the shape (and size) of a body:
- Example: When you inflate a balloon, the force of the air pressure stretches the rubber of the balloon, increasing its size.
Balanced and Unbalanced Forces:
a) Definitions and Examples:
- Balanced Forces:
- These are forces that act on an object in opposite directions with equal magnitudes.
- They cancel each other out, resulting in no net force acting on the object.
- Consequently, the object's state of motion does not change.
- Examples:
- A book lying on a table: The force of gravity pulling the book down is balanced by the normal force exerted by the table pushing the book up.
- A tug-of-war with equal teams: The forces exerted by each team on the rope are equal and opposite, resulting in no movement of the rope.
- Unbalanced Forces:
- These are forces that act on an object in different directions or with unequal magnitudes.
- They do not cancel each other out, resulting in a net force acting on the object.
- This net force causes a change in the object's state of motion.
- Examples:
- Kicking a football: The force of your foot on the ball is an unbalanced force, causing the ball to move.
- Applying brakes to a car: The friction between the tires and the road is an unbalanced force, causing the car to slow down.
b) Rubber Ball Example:
When you press a rubber ball between your hands, unbalanced forces act on the ball.
- Force 1: Your hand pushing on one side of the ball with a certain magnitude.
- Force 2: Your other hand pushing on the opposite side of the ball with an equal magnitude.
Although the forces are equal in magnitude, they act in opposite directions. Therefore, they are unbalanced, resulting in a net force that compresses the ball, causing its shape and size to change.
This example demonstrates how unbalanced forces can cause deformation in objects.
40. (a) What happens to the passengers travelling in a bus when the bus takes a sharp turn ? Give reasons for
your answer.
(b) Why are road accidents at high speeds very much worse than road accidents at low speeds ?
Answer:
(a) Passengers in a Bus Taking a Sharp Turn:
When a bus takes a sharp turn, the passengers experience the following:
- Inertia: Passengers tend to continue moving in the original direction due to inertia, which is the tendency of an object to resist changes in its state of motion. This results in them feeling a force pushing them outwards in the opposite direction of the turn.
- Centrifugal Force: Due to the circular motion of the bus, passengers experience a force outwards, called the centrifugal force. This force is not real but arises from the inertia of the passengers.
- Friction: The friction between the seat and the passengers' clothes helps them resist the outward force and prevents them from falling off the seat.
Therefore, passengers feel a force pushing them outwards during a sharp turn. This can cause them to lose balance, stumble, or fall if they are not holding on firmly.
(b) Road Accidents at High Speeds:
Road accidents at high speeds are much worse than accidents at low speeds for several reasons:
- Increased momentum: A vehicle's momentum (mass x velocity) is directly proportional to its speed. At high speeds, the momentum is significantly greater, resulting in a larger impact force during a collision. This translates to greater damage to vehicles and injuries to passengers.
- Reduced reaction time: Drivers at high speeds have less time to react to potential hazards and take evasive action. This reduces their chances of avoiding an accident altogether.
- Increased energy dissipation: During an accident, the kinetic energy of the vehicle needs to be dissipated. At high speeds, this energy is much greater and requires more distance and force to dissipate. This can lead to more severe damage and secondary collisions.
- Less time for airbags and other safety features to deploy: Airbags and other safety features have limited deployment times. At high speeds, the impact may occur before these features have a chance to activate, reducing their effectiveness in cushioning the impact.
- Increased potential for rollovers: At high speeds, vehicles are more susceptible to rollovers during accidents. Rollovers can cause additional injuries and fatalities due to the increased G-forces and the potential for ejection from the vehicle.
Therefore, it is crucial to maintain safe driving speeds to minimize the risks and severity of road accidents.
Multiple Choice Questions (MCQs)
41. When a toothpaste tube is squeezed, its shape changes. The force responsible for this is an example of :
(a) balanced forces (b) centripetal forces (c) unbalanced forces (d) centrifugal forces
(a) balanced forces
Explanation: When you squeeze a toothpaste tube, the force applied by your fingers is balanced by the forces exerted by the toothpaste inside the tube. This results in a change in shape without any change in the overall motion of the tube.
42. The inertia of an object tends to cause an object :
(a) to increase its speed (b) to decrease its speed
(c) to resist a change in its state of motion (d) to decelerate due to friction
(c) to resist a change in its state of motion
Explanation: Inertia is the tendency of an object to resist any change in its state of motion, whether it's at rest or in motion.
43. When we talk of a force acting on a body, it usually means :
(a) electrical force (b) balanced force (c) unbalanced force (d) nuclear force
(c) unbalanced force
Explanation: When we talk about a force acting on a body, we usually refer to an unbalanced force that causes a change in the object's state of motion.
44. A passenger in a moving train tosses a coin which falls behind him. This shows that the motion of train is :
(a) accelerated (b) uniform (c) retarded (d) along circular track
(a) accelerated
Explanation: The coin falling behind the passenger indicates that the train is accelerating forward. If the train were moving at a constant speed (uniform), the coin would fall straight down.
45. ‘When a hanging carpet is beaten with a stick, the dust particles start coming out of it’. This phenomenon
can be best explained by making use of :
(a) Newton’s third law of motion (b) Newton’s law of gravitation
(c) Newton’s first law of motion (d) Newton’s second law of motion
(c) Newton's first law of motion
Explanation: Newton's first law of motion states that an object at rest will stay at rest and an object in motion will stay in motion with a constant velocity unless acted upon by an unbalanced force. When you hit the carpet, you apply an unbalanced force to the dust particles, causing them to overcome their inertia and fly off.
46. A water tanker filled up to two-thirds of its tank with water is running with a uniform speed. When the
brakes are suddenly applied, the water in its tank would :
(a) move backward (b) move forward (c) rise upwards (d) remain unaffected
(b) move forward
Explanation: Due to inertia, the water in the tanker will continue to move forward even when the brakes are applied, causing it to splash towards the front of the tank. This phenomenon is known as the "surge" effect.
47. If we release a magnet held in our hand, it falls to the ground. The force which makes the magnet fall
down is an example of :
(a) balanced force (b) unbalanced force (c) magnetic force (d) muscular force
(b) unbalanced force
Explanation: The force of gravity pulling the magnet down is greater than any opposing force, making it an unbalanced force.
48. The inertia of a moving object depends on :
(a) momentum of the object (b) speed of the object
(c) mass of the object (d) shape of the object
(c) mass of the object
Explanation: The inertia of an object is directly proportional to its mass. A more massive object has more inertia and is more difficult to move or stop.
49. When a rubber balloon held between the hands is pressed, its shape changes. This happens because :
(a) balanced forces act on the balloon (b) unbalanced forces act on the balloon
(c) frictional forces act on the balloon (d) gravitational forces act on the balloon
(a) balanced forces
Explanation: When you press on the balloon, the forces you apply on both sides are equal and opposite, making them balanced forces. However, these forces cause a change in the shape of the balloon due to the nature of the material.
50. Which of the following effect cannot be produced by an unbalanced force acting on a body ?
(a) change in speed of the body (b) change in shape of the body
(c) change in direction of motion of the body (d) change in state of rest of the body
(b) change in shape of the body
Explanation: Unbalanced forces can cause changes in speed, direction, and state of rest of an object. However, they cannot cause a change in the shape of a perfectly rigid body.
Questions Based on High Order Thinking Skills (HOTS)
51. A plastic ball and a clay ball of equal masses, travelling in the same direction with equal speeds, strike
against a vertical wall. From which ball does the wall receive a greater amount of momentum ?
Answer:
Since both the balls have equal masses and are travelling in the same direction with equal speeds, they will have equal momentum. When they strike the wall, the wall will receive equal amounts of momentum from both the balls, regardless of whether they are made of plastic or clay.
Here's why:
- Momentum (p) is the product of mass (m) and velocity (v): p = mv.
- In this case, both balls have the same mass and velocity, so their momentum will be the same.
- Regardless of the material (plastic or clay), the momentum transferred to the wall only depends on the mass and velocity of the impacting object. The material properties wouldn't affect the total momentum transferred.
Therefore, the wall will receive the same amount of momentum from both the plastic ball and the clay ball.
52. A moving bicycle comes to rest after sometime if we stop pedalling it. But Newton’s first law of motion says
that a moving body should continue to move for ever, unless some external force acts on it. How do you
explain the bicycle case ?
Answer:
The bicycle stopping after you stop pedalling is actually in perfect agreement with Newton's first law of motion. While the law states that a moving body will continue moving forever unless acted upon by an external force, it's important to understand that the existence of "friction" is the key point here.
Here's how it works:
- Initial Motion: When you pedal the bicycle, you apply a force that overcomes the frictional forces acting against the wheels and other parts. This net force causes the bicycle to accelerate and maintain its motion.
- Stopping pedalling: When you stop pedalling, the external force provided by your legs is removed. However, the frictional forces remain, acting constantly against the movement of the bicycle.
- Friction's impact: These frictional forces, like the rolling resistance between the tires and road, air resistance, and internal friction within the bicycle's components, gradually slow down the bicycle.
- Equilibrium: As the frictional forces continue to act, they eventually balance out the residual momentum of the bicycle. This state of equilibrium brings the bicycle to a complete stop.
Therefore, even though the bicycle appears to be moving on its own, it's actually the external force of your pedalling that overcomes the frictional forces and keeps it moving. Once that external force is removed, the frictional forces take over and bring the bicycle to rest, completely in line with Newton's first law.
53. A man throws a ball weighing 500 g vertically upwards with a speed of 10 m/s.
(i) What will be its initial momentum ?
(ii) What would be its momentum at the highest point of its flight ?
Answer:
(i) Initial Momentum:
Formula:
Momentum (p) = mass (m) * velocity (v)
Given:
- Mass (m) = 500 g = 0.5 kg
- Velocity (v) = 10 m/s
Calculation:
p = 0.5 kg * 10 m/s = 5 kg m/s
Therefore, the initial momentum of the ball is 5 kg m/s.
(ii) Momentum at the Highest Point:
At the highest point of its flight, the ball's velocity is momentarily zero because it has overcome the force of gravity and reached the peak of its trajectory.
Therefore, using the same formula for momentum:
p = 0.5 kg * 0 m/s = 0 kg m/s
Therefore, the momentum of the ball at the highest point of its flight is zero.
54. A car is moving on a level road. If the driver turns off the engine of the car, the car’s speed decreases
gradually and ultimately it comes to a stop. A student says that two forces act on the car which bring it to
a stop. What could these forces be ? Which of these two forces contributes more to slow down and stop the
car ?
Answer:
The student is correct. Two main forces act on the car to slow it down and eventually stop it:
1. Rolling Resistance: This is the force that opposes the forward motion of the wheels due to their contact with the road. It arises from the slight deformation of the tires and the road surface, causing energy dissipation as heat.
2. Air Resistance: This is the force that opposes the forward motion of the car due to its movement through the air. It depends on the speed and shape of the car and increases significantly at higher speeds.
Both forces contribute to stopping the car, but their relative contributions can vary depending on the speed and conditions.
At lower speeds:
- Rolling resistance plays a more significant role as it is directly proportional to the speed.
- Air resistance becomes less significant as its effect increases with the square of the speed.
At higher speeds:
- Air resistance becomes increasingly dominant as it increases quadratically with speed.
- Rolling resistance, although still present, becomes less influential compared to air resistance.
Therefore, rolling resistance contributes more to slowing down the car at lower speeds, while air resistance becomes more dominant at higher speeds.
Additionally, other minor forces may also play a role, such as:
- Internal friction: Friction within the car's engine, drivetrain, and bearings consume energy and contribute to slowing the car.
- Brakes: If the driver applies the brakes, this will significantly increase the force opposing the car's movement and bring it to a faster stop.
Overall, the interaction of various forces, primarily rolling resistance and air resistance, ultimately slows down and stops the car when the engine is turned off.
55. There are two types of forces X and Y. The forces belonging to type X can produce motion in a stationary
object but cannot change the shape of the object. On the other hand, forces belonging to type Y cannot
produce motion in a stationary object but can change the shape of the object. What is the general name of
the forces such as (a) X, and (b) Y ?
Answer:
The general name of forces is:
(a) X: Unbalanced forces (b) Y: Balanced forces
Explanation:
- Unbalanced forces: These are forces that act on an object with different magnitudes or in opposite directions. They result in a net force, causing the object to move or change its speed or direction. Examples include pushing a book across a table, kicking a football, or applying brakes to a car.
- Balanced forces: These are forces that act on an object with equal magnitudes and in opposite directions. They cancel each other out, resulting in no net force and therefore no change in the object's state of motion. However, the forces can still cause deformation or change the shape of the object. Examples include squeezing a rubber ball, pressing a book against a table, or standing on the ground.
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