very quick question on gravity and work in Physics

[waytogo1]

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Hi there!
I have a very quick question on gravity and work...
In the explanations for #331 EK 1001 for Physics,
it says : "since work is the change in energy due to a force a conservative force only does work if we pretend that the potential energy associated with conservative force does not exist"
what does this mean exactly? I do not understand this explanation...

Thank you in advance!🙂

 

[DrknoSDN]

EK audio osmosis explains that one.

It summarizes that if you a exam questions asks you about the work done by dropping an object with mass (M) from height (H), in order to actually get a quantifiable number you must assume that W = mgh however that is not really correct when a conservative force like gravity acts on an object.

Work is the change in "total" energy, so as the object is falling due to gravity the total energy (kinetic + potential) is constant. And if energy is constant then no work is done by gravity. You would need to pretend that when you dropped the object it's potential energy was zero... That way you can calculate the work "done by gravity" via w=mgh.