题目

在水平道路上匀速行驶的汽车，受到扰动后车上的货物随车厢底版上下振动，设货物的振动是简谐运动且振动过程中物体不脱离底版。取竖直向上的方向为位移的正方向，振动图线如图所示，在图线上取a、b、c、d四点，则下列说法正确的是A． a点对应的时刻货物对车厢底板的压力最小B． b点对应的时刻货物对车厢底板的压力可能为零C． c点对应的时刻货物对车厢底板的压力最小D．d点对应的时刻货物对车厢底板的压力等于货物的重量阅读下列短文，从每题所给的选项中选出最佳答案。Today people are paying more and more attention to improving their health through sports and exercise. But some of them have some wrong ideas about it.A plate of chicken is a good meal before games because it has much energy.In fact, the best meal before games should have carbohydrates(碳水化合物). Foods like potatoes, bread, bananas are rich in it, chicken and meat are not. Carbohydrates are the best and most easily used forms of energy. The energy that you get for today’s game is from what you ate yesterday.The best time to exercise is early in the morning.Morning is a good time to exercise, but it may not be suitable for you. If an afternoon or evening period suits you, and you enjoy the feeling of getting healthier, you can choose any time to exercise. There is no fixed time for you to exercise.If you drink water when you exercise, you’ll get headaches and feel tired.The fact is that you must have some water during breaks when you exercise. And after exercising, you must have enough water. If you don’t drink enough water, then you’ll probably get headaches and feel tired.Exercising the same body part every day is the fastest way to improve strength.False! Exercising the same body part every day is the fastest way to cause problems. To improve strength, you want to work your muscles(肌肉) hard, but then you need to give those muscles a day of rest. Too much exercise can cause serious problems to muscles.Girls who do strength training will make their muscles big.Wrong! We usually connect those big muscles with bodybuilders(健美运动员), but girls don’t have enough male hormone(雄性激素) to make their muscles big like men. Strength training is a good way to make their muscles strong for girls.1.You had better eat ______ before games.A. bananas B. meatC. beef D. chicken2.You can ______ to improve arms’ strength.A. exercise your arms every dayB. eat enough chickenC. get enough male hormoneD. exercise your arms hard but rest for some time3.The writer advises you to ______.A. take exercise only in the morningB. become a bodybuilder by strength trainingC. drink enough water after exerciseD. make your muscles small through exercise4.According to the passage, which of the following is NOT true?A. Afternoon is the best to exercise as it’s cool.B. You can exercise at any time.C. It’s good for both girls and boys to do strength training.D. You should eat food full of energy today for tomorrow’s game.5.What is this passage mainly about?A. Reasons for sports and exercise.B. False ideas about sports and exercise.C. Result of games and exercise.D. Proper time for sports and exercise.