M2- Work-energy principle explanation

So in M2 I'm fairly ok with most parts of the course, however I commonly get questions wrong on ones in which it says to use the work energy principle. I understand that energy cannot be lost from the system and so on...however my problem is knowing what equation to make using the theory.

For example Loss in GPE=Gain in KE +/- work done...how do I know whether it is +/- or whatever. If someone could give a good explanation as to how to make this easier that would be great, thanks.

Reply 1

Nirgilis

14

Moved to maths for you :smile:

*bump*

Original post by podrodow1

So in M2 I'm fairly ok with most parts of the course, however I commonly get questions wrong on ones in which it says to use the work energy principle. I understand that energy cannot be lost from the system and so on...however my problem is knowing what equation to make using the theory.

For example Loss in GPE=Gain in KE +/- work done...how do I know whether it is +/- or whatever. If someone could give a good explanation as to how to make this easier that would be great, thanks.

I suggest that you use the approach
(PE + KE) at start + work done on the object - Work done against friction or resistance = (PE + KE) at the end.

WD on object means if there is an engine or the cyclist is pedalling or something is giving it a push or pull. You need to take a level as the zero level for the PE.

Reply 4

Coloneltreavy

1

Try this.
Total Work Done=KE+PE+Resistance(Friction, wind and such)+-Gravity(+if against direction of motion after resolving. -if in direction of motion after resolving).

This usually works well for me.

Reply 5

davros

16

Original post by Mutleybm1996

*bump*

Original post by tiny hobbit

I suggest that you use the approach
(PE + KE) at start + work done on the object - Work done against friction or resistance = (PE + KE) at the end.

WD on object means if there is an engine or the cyclist is pedalling or something is giving it a push or pull. You need to take a level as the zero level for the PE.