Electricity,likeotherformsof______,hasgreatlyincreasedinpriceinrecentyears. A: pressure B: force C: strength D: energy

中国大学MOOC: A particle of mass m is exerted with a force. Which of the following forces is not a conservative force?(g, k, C, D and γ are constants, and υ is the speed of particle.)

Which<br/>of the following is a competitive force under the five forces model? A: past rivalry with competitors B: predictable changes in the market C: vertical integration D: threat of substitutes

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.

The description of "Force field analysis" is NOT right A: A planning technique that helps identify the significant forces that influence a problem B: It begins with the supposition that any particular situation is the result of dynamic forces that create that situation. C: There are two types of forces acting upon any situation according to "Force field analysis". D: It is a scientific way to make a compromise