下列说法中正确的是（） A．做曲线运动的物体的速度一定是_爱下问搜题

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问题选择题

下列说法中正确的是（　　）

A．做曲线运动的物体的速度一定是变化的

B．做曲线运动的物体的动能一定是变化的

C．物体在恒力作用下，不可能做机械能守恒的运动

D．物体在变力作用下，不可能做机械能守恒的运动

答案

A、做曲线运动的物体的速度一定是变化的，由于存在加速度，且加速度与速度方向不共线．故A正确；

B、做曲线运动的物体的速度一定是变化的，但动能不一定变化，故B不正确；

C、物体在恒力作用下，可能机械能守恒也可能不守恒的．若恒力是重力，则守恒．故C不正确；

D、物体在变力作用下，但只有重力做功，所以机械能守恒，故D不正确；

故选：A

单项选择题

The grid computing is a new (66) technology connecting the distributed and (67) resources to the high-speed network and integrating a super-computer of processing capacity. The significance and architecture of the grid computing is explained. Several kernel technology such as OGSI, resource management, task management, task scheduling, high rate communication and security are described. Aiming at the particularity of the grid computing environment a mechanism similar to the technology of the search engine is designed to registry, discovery and (68) the resources in the grid. The whole model of the resource management is built by connecting task manager in the local resource management system to others with P2P model. The task may migrate among the task managers in order to (69) the load. The task users summit may be executed in relatively tight resource set, which will not only decrease the total communication overheads of the whole task but also (70) the performance of the system.

（68）是（）

A. search for

B. find

C. look for

D. locate

问答题简答题

铁路工程量清单计价与地方定额计价有何区别？