21. 質量為m1、m2 (m1＞m2)之兩物體繫於繩之兩端，並跨過一質量可忽略之定滑輪，當滑輪以加速度a上升時，繩之張力為何？

6. Given that the enthalpy required to convert CHCl3(g) to gaseous C, H, and Cl atoms is 1397 kJ/mol and that the dissociation enthalpy of a C-H bond is 413 kJ/mol, what is the bond dissociation enthalpy of a C-Cl bond？ (A)328 kJ/mol　(B)603 kJ/mol　(C)984 kJ/mol　(D)1397 kJ/mol