Work, energy and power

• Work done - when force is applied on a body and it covers some displacement in the direction of force applied work is said to be done
• Work = force × displacement

  W = F × S

  W = FScos0 ( theta = direction of work done)
• Work is a scalar quantity

  It's SI unit is joule
• Types of work

  • POSITIVE WORK DONE - work done is positive when direction of force and displacement is same and angle b/w them is acute ( less than 90°) ( cos0 = 1)
• NEGATIVE WORK DONE - work is negative when the direction of force applied and displacement is different and the angel b/w them is obtuse ( more than 90°) ( cos180 = -1)
• ZERO WORK - work done is zero if force applied does not cause any displacement and the force and displacement are mutually perpendicular to each other ( thetha = 90 ) ( cos90 = 0)
• CONSERVATIVE FORCES - a force is said to be conservative if work done by or on the force does not depend upon the path followed but only on the final and initial position.

  • Work done by on against the body in a round trip ie final and initial position areare same is always zero
  • Eg gravitational force, electrostatic force
• • NON CONSERVATIVE Forces - a force is said to be non conservative if work done on or by the force depends upon the path followed and final and initial positions
  • The work done by or on the force is not zero but 2W in a round trip
• Work done using graph

  
• ENERGY- is the capacity or ability of a body to do work

  • It is a scalar quantity
  • SI unit is joule
  • Energy is the property of a system
• Mechanical energy = potential energy + kinetic energy
• Types of mechanical energy

  1. Potential energy - is the energy possessed by a body due to its position and configuration when any work is done on a body it is stored in the form of potential energy
  2. Kinetic energy-is the energy possessed by a body due to its motion inin general potential energy of a body gets converted into kinetic energy when it is in motion
• KE =1/2mv^2
• Hooke's law - states that the displacement of extension is directly proportional to force applied

  F=kx (where k is spring constant)
• Potential energy stored in a spring  =

  U = 1/2kx^2
• WORK ENERGY Theorem - states that net work done by the force is equal to the kinetic energy of a body

  W= 1/2mv^2 - 1/2mu^2

  W=∆k
• Total mechanical energy of a body is always conserved
• POWER - is the rate of doing work or the rate of transferring energy

  
• Power is a scalar quantity and it's SI unit is Watt
• Principle OF CONSERVATION OF ENERGY - energy can neither be created nor be destroyed but it can only be transferred from one form to another.
• COLLISION - IS THE PROCESS OF TWO OR More BODIES COLLIDING WITH EACH OTHER AND THEY EXERT A STRONG FORCE ON EACH OTHER
• ElASTIC COLLISION - it is the type of collision in which there is no loss of kinetic energy during collision

  • Total momentum is conserved
  • Total kinetic energy is conserved
  • Total energy of the system is conserved
• INELASTIC COLLISION - is the type of collision in which KE is lost during the collision

  • The total energy is conserved
  • The total momentum is conserved
  • The total KE is not conserved
• PERFECTLY INELASTIC COLLISION- after collision two bodies stick together and move with the same velocity
• HEAD ON COLLISION - In such type colliding bodies move in same direction after collision
• OBLIQUE OR 2D COLLISION - when two bodies after collision do not move in same direction after collision but in the same plane