Important points :-

1:- Kinetic energy (KE) doesn’t depend upon direction of motion & it is never negative.

2:-As velocity is a frame depend quantity therefore KE also depends on reference frame.

3:-KE of a system can be increased or decreased without applying any external force of the system by the use of internal energy. For eg- bomb.

4:-Work done (WD) by all Forces on a system equal the change in KE.

5:-Work done by external force on a system equals the change in its total energy (TE).

6:-Negative of the WD by the conservative internal force on a system equals to change in PE.

7:-NO work is done by a force on an object if- 

  • The force is always perpendicular to its velocity.
  • The object is stationary but the point of application of the force moves on the object.
  • The object moves in such a way that the point of application of the force remain fixed.

8:-Work, Energy theorm depends upon reference frame.

9:-Body can have mechanical energy without having momentum & also can have momentum without mechanical energy. i.e. [ KE=O , TE=PE][KE =-PE, TE=O].

10:-It is possible to exert a force which does work on a body without changing its KE.

11:-In spring block system maximum velocity is when (Fnet = O or a=o ) is at mean position.

12:-If a block of mass M slides down a plane inclined at an angle ∅ increasing the angle will not increase the energy lost due to friction.

13:-When a conservative force does the positive (+ive ) work on a body the PE decreases.

14:-PE of a simple pendulum is Max when it is the turning points of the oscillation.

  • WD by gravity is negative (-ive ) that mean PE increases & KE decreases.
  • Positive WD means KE & P(momentum) both increases.

15:-Mechanical energy of a body can be negative if PE>KE

16:-It is physically not possible to have situation when (E-U<O)

17:-Internal force can change KE & ME but can’t change the TE & MOMENTUM.

18:-When two particle collide and stick together only energy is conserved & work is negative. As ME & KE is not conserved.


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