1st Year Physics Chapter 4 Notes

• Important from 1st year physics chapter 4 mcqs with answers Punjab Textbook.
• Work done by a constant force: Let us consider an object which is being pulled by a constant force F at an angle e to the direction of motion. The force displaces the object from position A to B through a displacement d. We define work W done by the force F as the scalar product of F and d.  W= F.d=Fd cos = (F cose) d . The quantity (F cose) is the component of the force in the direction of the displacement d. Thus, the work done on a body by a constant force is defined as the product of the magnitudes of the displacement and the component of the force in the direction of the displacement. 
• Can you tell how much work is being done? On the pail when a person holding the pail by the force F is moving forward (Fig. 4.2 a). On the wall (Fig. 4.2 b)?
• When a constant force acts through a distance d, the event can be plotted on a simple graph (Fig. 4.3). The distance is normally plotted along x-axis and the force along y-axis. In this case as the force does not vary, the graph will be a horizontal straight line. If the constant force F (newton) and the displacementd (metre) are in the same direction then the work done is Fd (joule). Clearly shaded area in Fig. 4.3 is also Fd. Hence the area under a force- displacement curve can be taken to represent the work done by the force. In case the force F is not in the direction of displacement, the graph is plotted between F cos) and d.
• From the definition of work, we find that:
• (i) Work is a scalar quantity.
• (ii) If 90°, work is done and it is said to be positive work.
• (iii) If 0=90°, no work is done.
• (iv) If > 90°, the work done is said to be negative.
• (v) Sl unit of work is N m known as joule (J).
• Important from 1st year physics chapter 4 solved exercise Punjab Textbook.
• Work done by a variable force: In many cases the force does not remain constant during the process of doing work. For example, as a rocket moves away from the Earth, work is done against the force of gravity, which varies as the inverse square of the distance from the Earth's centre. Similarly, the force exerted by a spring increases with the amount of stretch. How can we calculate the work done in such a situation?  Fig. 4.4 shows the path of a particle in the x-y plane as it moves from point a to point b. The path has been divided into n short intervals of displacements Ad,, Adz, ... Ad and F1. F2........ F are the forces acting during these intervals. During each small interval, the force is supposed to be approximately constant. So the work done for the first interval can then be written as and in the second interval AW, F1. Ad₁ = F, cose, Ad, = AW2F2.Ad₂ = F₂ cos d.
• Work done by a gravitational field
• Definition of Power with formula
• Power and Velocity
• Energy and its types
• Kinetic energy and potential energy
• Work- Energy Principle
• Absolute Potential Energy
• Escape Velocity                                                                         
• Interconservation of Potential energy and kinetic energy
• Conservation of energy
• Important from 1st year physics chapter 4 long questions Punjab Textbook.
• Non-conservation energy sources
• Energy from Tides
• Energy from waves
• Solar energy
• Energy from biomass
• Energy Waste products
• Geothermal energy
• Important from 1st year physics chapter 4 important long questions Punjab Textbook.