一、选择题(15分)每小题3分。每小题选出一个正确的答案,把它的号码填写在题后的方括号内。选对的,得3分;选错的,得-1分;不答的,得0分;如选了两个答案,不论写在括号内或括号旁,得-1分。 (1)一质点作简谐振动,其位移x与时间t的关系曲线如图1所示。由图可知,在t=4秒时,质点的 One, multiple-choice questions (15 points) 3 points for each question. Select a correct answer for each question and fill in the number in square brackets after the question. If you choose the right one, you get 3 points; if you choose the wrong one, you get -1 point; if you don’t answer, you get 0 point; if you choose two answers, you get -1 points regardless of whether they are enclosed in parentheses or brackets. (1) The harmonic vibration of a mass point, the displacement x and time t curve shown in Figure 1. The figure shows that at t=4 seconds, the mass