Quarter 4

• Projectile motion


  A form of motion where an object given an initial velocity is thrown or projected and is allowed to be acted on by gravity in a curved-like path
• Projectiles


  Objects that undergo projectile motion
• Trajectory


  The curved path followed by a projectile
• Projectile motion


  1. Horizontal motion (x-axis)

  2. Vertical motion (y-axis)
• Parts of projectile motion

  • Angle
  • Horizontal velocity
  • Height
  • Vertical velocity
  • Range
• An object projected along horizontal line that soon comes down has a vertical acceleration of -9.8m/s2 as it falls
• The angle of projection for a body to acquire the longest possible range should be 45°
• A ball hit at any angle has the least speed at its highest point in its flight
• Factors affecting how far a projectile will land

  • Angle of launch
  • Initial velocity
• Impulse


  The change of momentum experienced by a body
• Momentum


  The product of mass and velocity of a moving object
• Momentum is equal to the product of mass and velocity
• The unit for momentum is kg-m/s
• If an object of any mass is not moving, it has zero momentum since its velocity is zero
• Impulse


  The product of force and time
• Sample problem


  • A boy hits an approaching ball with a force of 750 N. If he hits the ball in 0.002 s, how much impulse is imparted to the ball?
• During collision, the two cars gained the same momentum but moved in opposite direction
• Since the cars have different masses, they will accelerate differently as stated in Newton's second law of motion
• Momentum before and after collision

  1. Before collision: 600 kg car moving at 5 m/s, stationary car of mass 500 kg

  2. After collision: total mass?, velocity?
• Law of conservation of momentum


  When two objects in an isolated system collide, the total momentum of the objects before the collision is equal to the total momentum of the objects after the collision
• Sample problem


  • Two 0.5 kg balls approach each other with the same speed of 1.0 m/s. What is the total momentum of the system before collision?
• When two objects collide and stick together the total momentum does not change
• When a large mass and a small mass objects collide head-on, the small mass object receives the greatest impulse
• The total momentum in an isolated system is conserved
• When two billiard balls approach each other at equal speed and collide in a perfectly elastic collision, their velocities after collision is same in magnitude but opposite in direction
• Energy


  The ability to do work
• Mechanical energy


  • The total energy of kinetic energy and potential energy in a system of objects
• Energy transformation example


  1. Chemical Energy

  2. Heat

  3. Mechanical Energy (with wasted heat)
• Examples of a potential energy being changed into kinetic energy


  • A cart rolling down a hill
  • A student lets go a stretched slinky
  • A twig falling from a branch
  • The spring of a broken toy shoots up
• Internal energy


  The total energy contained in an object, including kinetic and potential energy
• If we add heat to the system and the system does no work, we increase its internal energy increases
• First law of thermodynamics

  The change in internal energy of a system equals the net heat transfer into the system minus the net work done by the system
• Sample problem


  • While a gas does 400J of work on its surroundings, 900J of heat is added to the gas. What is the change in the internal energy of the gas?
• A block of metal feels colder to touch than a block of wood because heat flows more readily in denser materials like metals aside from metals being good conductors of heat
• Spontaneous process


  Occurs naturally
• Heat engine


  Converts thermal energy to mechanical energy
• Kilowatt


  The unit used for electrical consumption measured by electric companies for households
• Megawatt


  The unit used to measure power in power stations generating electricity
• Meter reading example


  • On July 1: 36121 kW
  • On July 31: 46165 kW
• Sample computation for electricity consumption

  • If the cost of electricity in Mangaldan is Php 6.50 per kWh, how much did electricity cost for January? Kilowatt used from January 1-31: 46165 - 36121 = 10,044 kWh. Cost of electricity: 10,044 kWh x Php 6.50 = Php 65,286.00