• # question_answer If only conservative forces are working in the system and we apply some external force A) ${{W}_{ext}}=\Delta U$(always)      B) ${{W}_{\text{conservative}}}=-\Delta U$(always) C) ${{W}_{ext}}=\Delta U+\Delta KE$ (always)    D) ${{W}_{\operatorname{co}nservative}}=-\Delta KE$

 [b] If only conservative forces are acting in the system. $\Rightarrow$ ${{W}_{ext}}=\Delta U$ (If body moves without acceleration) ${{W}_{ext}}=\Delta U+\Delta KE$ (if body moves with acceleration) $\Rightarrow$ ${{W}_{\text{conservative}}}=-\Delta U$ (always)