Which of the following expressions is not correct (不正确)?
A: If a system is only acted by conservative forces （保守力）, the mechanical energy（机械能）must be conserved （守恒）.
B: If net external force is zero then the linear momentum of the system must be conserved.
C: If net external force is zero, then the mechanical energy of a system must be conserved.
D: If net external force is zero, then the mechanical energy of a system may not be conserved.
A: If a system is only acted by conservative forces （保守力）, the mechanical energy（机械能）must be conserved （守恒）.
B: If net external force is zero then the linear momentum of the system must be conserved.
C: If net external force is zero, then the mechanical energy of a system must be conserved.
D: If net external force is zero, then the mechanical energy of a system may not be conserved.
举一反三
- The internal force of any structure is zero if it is not subjected to external loads.
- The internal force of any structure is zero if it is not subjected to external loads. A: 正确 B: 错误
- Which forces belong to external forces(). A: spring force B: damper force C: actuator force D: gravity force
- Which of the following is not an external force of change?
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