Question

i always have a problem in identifying the conservative force and non conservative force in work energy chapter

Answer 1

Conservative force are the forces which conserve energy and non- conservative force are the force in which energy is wasted.
 an example of conservative force is if an object is falling from an height from an straight path of 7 m and an curved path 18 m and  both displacement is same than we will see that in both cases energy is same.Potential and kinetic energy are the example
Now, in non - conservative force move an object  on an plane surface from A to B, move it continuously for four to five times from A to B.We will see that heat is generated.
,so from this we conclude that energy is not conserved but some converted into heat this non - conservative energy,example is frictional energy

Answer 2

Conservative forces are forces, where the net work done in a round trip is 0. For e.g., gravity. If a body is lifted and dropped by height 'h', then net work done by gravity is mg(h-h) = 0. 
However, non-conservative forces are forces, which are not conserved. i.e, in a round trip, the net wok done is not 0. Common examples of such forces are friction and induced electricity. 


For your benefit, almost all other types of forces are conservative, apart from the 2 mentioned above. Also, conservative forces have the concept of P.E (potential energy) associated with it, whereas P.E for a non-conservative force is undefined