Question

Deduce how work done is related to energy when
1 - friction is present
2 when friction is not present

Answer 1

Do you know what mechanical energy is?
Do you know under which conditions it is conserved?

Answer 2

mechanical energy is the energy of a body , total energy sum of k.e and p.e
and it is conserved when there is no opposing force i guess

Answer 3

It is conserved when there is no force acted by an operator and when there is no dissipative phenomenon that could convert some of this energy to thermal energy.

Answer 4

If the net work done by nonconservative forces is zero, the total mechanical energy of an object is conserved; that is, it doesn’t change. (If, on the other hand, friction or another nonconservative force is present, the difference between ME2 and ME1 is equal to the net work the nonconservative forces do: ME2 – ME1 = Wnc.) ME2 and ME1 are the mechanical energies of the system at different points, Wnc is the work done by the nonconservative force, in this case, friction: Wnc = Force * Distance.

Answer 5

but i didn't got what i asked

Answer 6

When only conservative forces act:

work done on object = change in energy of object

Friction is nonconservative, so the above will not be true (energy is lost as heat/sound etc)

Answer 7

Well, in any case Total work done on the system is equal to the change in the system's kinetic energy.

This statement is true whether friction is present or not, in the sense that total work includes work done by the friction forces, if any.