题目

When you look at your meals, some ingredients (原料) are easy to see. But your meals are also filled with ingredients you can’t see. Salt is a perfect example of an ingredient that you might not notice, even when you eat a lot of it. But it’s the salt we can’t see that concerns scientists most. For years, doctors have warned patients that too much salt can be bad for their health. Heart trouble has long been considered a grown-up problem. New research suggests that salt is starting to affect kids. And salt isn’t the only cause of high blood pressure. Eating lots of junk food, （6分）如图所示为用打点计时器验证机械能守恒定律的实验装置。（1）关于这一实验，下列说法正确的是（ ）A.重锤的质量不必测量B.打点计时器应接低压直流电C.应先接通电源打点，后释放纸带D.需使用秒表测出重物下落的时间（2）选用实验中得出的一条纸带来验证机械能守恒定律。图中O点为起始点，A,B,C,D,E,F,G为七个相邻的原始点，F点是第个点。设相邻点间的时间间隔为，下列表达式可以用本实验中计算F点速度的是（ ）A.B.C.D.