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?
- What does the autopilot system include?? Hydraulic system|Mechanical system|Electrical system|All of above
内容
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The surroundings include everything external to the system，and the system is separated from the surroundings by the system boundaries.
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The crankshaft and connecting rod converts energy into energy used to drive the vehicle. A: mechanical, thermal B: mechanical, kinetic C: thermal, mechanical D: kinetic, mechanical
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What’s the type of the control system on CFM56-3 engine? ( ) A: pneumatic mechanical system B: EEC system C: FADEC system D: hydro-mechanical system
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It consists of mechanical system, hydraulic system, electrical system and electronic control system, all working together in perfect harmony．
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Which of the following descriptions is correct? A: The microscopic viewpoint studies the large-scale properties of matter (temperature, pressure, volume, etc.). B: The part of the universe under study in thermodynamics is called the system; the parts of the universe that can interact with the system are called surroundings. C: For an open system, only matter can be transferred between system and surroundings. D: A closed system must be an isolated system, but an isolated system may not be a closed system.