题型：问答题 如图所示，长为、倾角为θ的光滑绝缘斜面处于水平向右的匀强电场中，一电荷量为+q、质量为m的小球以初速度,由斜面底端的M点沿斜面上滑，到达斜面顶端N的速度仍为，则 ：A．小球在N点的电势能小于在M点的电势能B．M、N两点的电势差为C．电场强度等于2D．电场强度等于 查看答案
题型：问答题 The safety of ships at sea does not depend only on the arrangements made in the ships themselves. Dangerous coasts and rocks may be seen in the daytime, (51) they are a threat to safe navigation at night. Lighthouses are therefore erected at such places to (52) sailors of the danger. Modern lighthouses are put up at all dangerous places near the courses (53) by ships. On some rocky coasts several lighthouses may be built not far from each other, and (54) the sailors on a ship may know which is which, they have (55) arrangements of lights. One lighthouse will give a single flash at regular (56) , another may give two flashes; a third may give two followed by one; and so on. (57) watching the lights the navigator is able to decide exactly where he is, and he can set his (58) with confidence. In the approaches to some ports two continuous lights are set up, one above (59) but some distance behind; when they appear from the sea one above the other, the ship is on the right course; but if they do not, the captain knows that he is (60) his course and likely to strike a rock or the bottom of the sea.A．warnB．predictC．announceD．show 查看答案
、倾角为θ的光滑绝缘斜面处于水平向右的匀强电场中，一电荷量为+q、质量为m的小球以初速度
,由斜面底端的M点沿斜面上滑，到达斜面顶端N的速度仍为，则 ：
