Class 9th Physics Chapter 3 Question Answer

Complete Notes of Class 9th Physics Chapter 3 Question Answer Dynamics Numerical in 9th Class Physics Urdu Medium written by Sir Fahad Abbas Suib. These computerized notes are very helpful in the preparation of Dynamics Numerical for students of the Class 9th Physics Chapter 3 Question Answer these are according to the paper patterns of all Punjab boards.

• Important Values and Important Formulas
• Dynamics Exercise Numericals with Solutions in Urdu
• NEWTON'S SECOND LAW OF MOTION: Newton's second law of motion deals with situations when a net force is acting on a body. It states that:
• "When a net force acts on a body, it produces acceleration in the body in the direction of the net force. The magnitude of this acceleration is directly proportional to the net force acting on the body and inversely proportional to its mass".
• MASS AND WEIGHT: Generally, mass and weight are considered similar quantities, but it is not correct. They are two different quantities. Mass of a body is the quantity of matter possessed by the body. It is a scalar quantity and does not change with change of place. It is measured by comparison with standard masses using a beam balance. On the other hand, weight of a body is the force equal to the force with which Earth attracts it. It varies depending upon the value of g, acceleration due to gravity. Weight woi a body of mass m is related by the equation w = mg  Weight is a force and thus it is a vector quantity. Its SI unit is newton (N); the same as force. Weight is measured by a spring balance.
• Newton's third law of motion class 9: Newton's third law of motion deals with the reaction of a body when a force acts on it. Let a body Aexerts a force on another body B, the body B reacts against this force and exerts a force on body A. The force exerted by body A on B is the action force whereas the force exerted by body B on A is called the reaction force. Newton's third law of motion states that: third law of motion class 9 "To every action there is always an equal but opposite reaction".
• FORCE AND THE MOMENTUM: Newton's second law of motion as "When a force acts on a body, it produces an acceleration in the body and will be equal to the rate of change of momentum of the body".nSI unit of momentum defined by newton-second (Ns) which is the same as kgms-1.
• LAW OF CONSERVATION OF MOMENTUM: Momentum of a system depends on its mass and velocity. A system is a group of bodies within certain boundaries. An isolated system is a group of interacting bodies on which no external force is acting. If no unbalanced or net force acts on a system, then according to its momentum remains constant. Thus the momentum of an isolated system is always conserved. This is the Law of Conservation of Momentum. It states that: "The momentum of an isolated system of two or more than two interacting bodies remains constant".
• Consider the example of an air-filled balloon as described under the third law of motion. In this case, balloon and the air inside it form a system. Before releasing the balloon, the system was at rest and hence the initial momentum of the system was zero. As soon as the balloon is set free, air escapes out of it with some velocity. The air coming out of it possesses momentum. To conserve momentum, the balloon moves in a direction opposite to that of air rushing out.
• "The force that opposes the motion of moving objects is called friction". Friction is a force that comes into action as soon a body is pushed or pulled over a surface. In case of solids, the force of friction between two bodies depends upon many factors such as nature of the two surfaces in contact and the pressing force between them. Rub your palm over different surfaces such as table, carpet, polished marble surface, brick, etc. You will find smoother is the surface, easier it is to move over the surface. Moreover, harder you press your palm over the surface, more difficult would it be to move.
• Why friction opposes motion?