Collegedunia Team Content Curator
Content Curator
A force is an effect that, unless counterbalanced by other forces, can cause a change in the velocity of the object, i.e., to accelerate.
- A force can change the state of rest or uniform motion of the body.
- It can change the direction as well as the shape and size of the body.
- All these effects can be observed when the force is in contact with the body hence we say this is a contact force.
- Muscular force, tension force, and frictional force are examples of contact force.
- Non-contact forces occur when objects do not make contact with one another or when a force is applied without interaction.
- Magnetic force, electrostatic force, and gravitational force are examples of non-contact force.
- The SI unit of force is Newton (N) and it is a vector quantity.
- The dimensional formula of force is [M L T-2].
Very Short Answers Questions [1 Mark Questions]
Ques. A body is moving along a straight path. What will happen to the body in the absence of an external force?
- It will move with the same speed in a different path
- It will move with a reduced speed along the same path
- It will move with the same speed along the same straight path
- It will stop
Ans. The correct answer is c. It will move with the same speed along the same straight path.
Explanation: If no external force is applied, then due to the inertia of motion of the body moving along a straight path, it will keep moving on the same straight path with the same speed.
Ques. Which of the following is the SI unit of force?
- kg m/s
- Ohm
- Newton-metre
- Newton
Ans. The correct answer is d. Newton
Explanation: The Si unit of force is Newton (N). A force of 1 Newton is defined as the force required by an object of mass 1 kg to accelerate it with an acceleration of 1 m/s2
Ques. Which of the following is true about force?
- Force can change the direction of an object.
- Force can change the shape of an object.
- Force can change the speed of an object.
- All of the above
Ans. The correct answer is d. All of the above
Explanation: Force can change the shape, speed, and direction of an object.
Ques. Which of these can a force acting on an object not change?
- State of rest
- Mass
- Direction of motion
- Shape
Ans. The correct answer is b. Mass
Explanation: Mass is an intrinsic property of a body and is defined as the measure of the matter inside a body. A force acting on a body does not change its mass.
Ques. Choose the correct statement(s):
Statement 1: Unbalanced forces can change the direction of motion of a body.
Statement 2: A balanced force is required to accelerate the body.
Statement 3: An object moves with a uniform velocity when balanced forces are acting on it or if there is no net force acting on it.
Statement 4: Balanced force cannot bring an object at rest to motion.
- Only statement 1
- Statements 1, 3 and 4
- Statements 1, 2 and 3
- Only statement 2
Ans. The correct answer is b. Statements 1, 3 and 4
Explanation: Balanced forces acting on an object cannot produce any change in the object's state of motion since the net force acting is zero. If the object is in motion, it will stay in motion; if the object is at rest, it will stay at rest. Forces acting on an object must be unbalanced in order to change its condition of rest or uniform motion.
Short Answers Questions [2 Marks Questions]
Ques. What is a force?
Ans. Force is defined in physics as the push or pull on a body that causes it to change its velocity.
- Force is an external agent that may change the condition of rest or motion of a body.
- It has a magnitude as well as a direction. The direction of the force is the point where force is applied, and the application of force is the point where force is applied.
- The SI unit of force is Newton (N).
Ques. What are the two types of forces in classical mechanics?
Ans. There are two types of forces in classical mechanics: contact forces and non-contact forces. Frictional force, tension force, normal force, and so on are examples of contact forces. Gravitational force, electrical force, magnetic force, etc. are examples of non-contact forces.
Ques. What is gravitational force?
Ans. Gravitational force is an example of non-contact force. It is a natural force that is always attractive and conservative. The force of attraction experienced by two or more objects due to their mass is defined as gravitational force. Gravitational force is calculated using the Gravitational Force Formula, which is derived from Newton's Universal Law of Attraction.
Ques. Why is Newton’s second law of motion not applicable to the motion of a rocket?
Ans. Mathematically, Newton’s second law of motion mathematically is given by
F = ma
Where m is the mass of the body and a is the acceleration produced.
This law is only applicable when the mass of the body remains constant. In the case of the motion of a rocket the mass of the rocket continuously decreases due to the burning of the fuel.
Also Read:
Long Answers Questions [3 Marks Questions]
Ques. What are the different types of fundamental forces in nature?
Ans. The following are the fundamental forces in nature
- Gravitational force: Gravitational force is the weakest fundamental force in nature. It is an attractive force produced by gravitational interaction. The gravitational force between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them, according to Newton's law of gravity.
- Electromagnetic force: The electromagnetic force is a physical interaction that takes place between electrically charged particles. It is the combined effect of all magnetic and electrical forces that act between charged particles. The electromagnetic force may be attractive and repulsive.
- Strong nuclear force: The strong interaction is a fundamental interaction that restricts quarks into proton, neutron, and other hadron particles. It is also known as the strong force or strong nuclear force.
- Weak nuclear force: The weak nuclear force is the second weakest force after gravity, and it also has the shortest range. Nuclear beta decay (by changing the flavor of quarks) and neutrino absorption and emission are caused by the weak nuclear force.
Ques. If a net force of 7 N was constantly applied to a 400 g object at rest, how long would it take to raise its velocity to 80 m/s?
Ans. Given
- Initial velocity of the object, u = 0
- Final velocity of the object, v = 80 m/s
- Force acting on the object, F = 7 N
- Mass of the object, m = 400 g = 0.4 kg
From Newton’s second law of motion, we have
F = ma
Where a is the acceleration produced in the object
⇒ a = F/m = 7/0.4 = 17.5 m/s2
Using the equation of motion, v = u + at, we get
Time, t = (v - u)/a
⇒ t = (80 - 0)/17.5 = 4.57 seconds
Ques. What are the characteristics of gravitational force?
Ans. The following are the characteristics of gravitational force
- The gravitational force between two bodies forms an action-reaction pair i.e. the forces are equal in magnitude but opposite in direction.
- Gravitational force is a central force i.e. it acts along the line joining the centres of the two interacting bodies.
- Gravitational force is a long-range force.
- Gravitational force is a conservative force.
Very Long Answers Questions [5 Marks Questions]
Ques. What are the differences between force and pressure?
Ans. The following are the differences between force and pressure
| Force | Pressure |
|---|---|
| Force is defined as the push and pull action on a body that results in acceleration. | The force applied perpendicular to the surface of an object per unit area across which that force is distributed is defined as pressure. |
| The SI unit of force is Newton (N). | The SI unit of pressure is Pascal (Pa). |
| Force acting on an object can be measured by a device known as a Dynamometer. | Manometers and barometers are the two most common pressure-measuring instruments. The barometer measures pressure in proportion to the surrounding atmospheric pressure. A manometer is used to measure fluid pressure in relation to an outside source, which is typically thought to be the Earth's atmosphere. |
| Force is a vector quantity, which implies it has both magnitude and direction. | Pressure is a scalar quantity, which implies it has no direction. |
| Force can be applied to the object's face, edges, sides, or vertices. | Pressure acts only on the object's surface or face. |
Ques. What are the various effects of force?
Ans. The following are the effects of force
- It has the ability to cause a motionless object to move: When force is applied to a stationary object, it tends to move in the direction of the force. For example, when a force is applied to a stationary tennis ball, the ball will continue to move in the direction of the applied force.
- It has the ability to stop a moving object: Force must be given to a moving object to either stop it or slow it down. For example, the motion of a moving ball can be stopped by applying an external force.
- It has the ability to change the speed of a moving object: When we continue to peddle the bicycle pedal, the speed of the bicycle rises. When we apply the brake, the bicycle's speed reduces.
- It has the ability to change the direction of a moving object: Any moving object's direction can be changed by applying an external force to that object. For example, exerting force at an angle may change the path of a moving football.
- It has the ability to change the shape or size of an object: The shape of a circular rod can be changed into a flat sheet by applying an external force on the rod by hammering the rod.
Ques. Explain force in Newton’s laws of motion.
Ans. Newton's laws of motion are commonly used to define the concept of force.
- According to Newton's first law of motion, a body moving at a constant speed in a straight line or at rest will remain in that state unless some external force is applied.
- The second law states that when an outside force acts on an object, the object experiences acceleration or a change in velocity in the direction of the force. The value of acceleration is proportional to the amount of matter in the body.
- According to Newton's third law, when one object exerts a force on another, the second object exerts an equal and opposite force on the first. This law explains why a force, whether it moves or not, tends to change the shape of an object.
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