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. 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!