what are the limitation work energy theorem ? this theorem is very helpful in solving questions. But I think there are some limitations of this bold theorem. that is (1) does not define the direction of velocity & (2) does not define spontaneity of process, like say there is an body on the floor, assume it's Potential energy to be zero(PEi) if we say that without any external force it attains height h and specific kinetic energy which sums(KEf+PEf) to be zero(PEi). Finally we can say that initial PEi= final KEf+final PEf. there is nothing in these statements according to conservation of energy / work energy theorem but even a child can say from his/her common sense that it is impossible. My question is is my second reason correct? & what are other limitation of this theorem? & differentiate between work energy theorem and conservation of energy. work energy theorem seems to be derived from law of conservation of energy.