Work done is defined as F vector. dx vector or F dx cos θ where θ is the angle between F vector and dx vector.(adsbygoogle = window.adsbygoogle || []).push({});

But, there is another common formula-

dU=-F.dx

Here, dU is the potential energy stored in the object on which the force is acting upon. (Am I correct?)

But, the work done on the object, gets stored in it as its internal energy (assuming no heat loss).

So.

In the case of pushing a block on a rough floor.

The force of friction acts opposite to displacement in this case, and so work done would be

F(r).dx cos 180 = -F(r).dx, i.e. negative.

But if we look at it from the energy stored formula, the energy stored in the object would be - (-F(r) dx) = F(r)dx., i.e. positive.

How come the two energies, although they represent the same thing, have different signs?

I am sensing that there is something very wrong with my understanding of things.

Help would be appreciated!

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# Understanding work done by friction

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