题目

Have you ever noticed that some people can eat what they want and stay in shape, while others carefully watch what they eat and still put on weight? How disappointing!【1】.Scientists say that when some people eat, their bodies will naturally store the extra energy from food as fat. 【2】Meanwhile, other people eat more than they need but their bodies are able to “burn off” the extra food without making fat, so they seldom have weight problems.To prove this, scientists have experimented on laboratory mice. They gave the mice a special diet with a lot of fat. Some mice gained weight whi某同学把附有滑轮的长木板平放在实验桌上，将细绳一端拴在小车上，另一端绕过定滑轮，挂上适当的钩码，使小车在钩码的牵引下运动，以此定量探究绳拉力做功与小车动能变化的关系．此外还准备了打点计时器及配套的电源、导线、复写纸、纸带、小木块等．组装的实验装置如图所示．①若要完成该实验，必需的实验器材还有哪些 ． ②实验开始时，他先调节木板上定滑轮的高度，使牵引小车的细绳与木板平行．他这样做的目的是下列的哪个（填字母代号）A．避免小车在运动过程中发生抖动B．可使打点计时器在纸带上打出的点迹清晰C．可以保证小车最终能够实现匀速直线运动D．可在平衡摩擦力后使细绳拉力等于小车受的合力③平衡摩擦后，当他用多个钩码牵引小车时，发现小车运动过快，致使打出的纸带上点数较少，难以选到合适的点计算小车的速度．在保证所挂钩码数目不变的条件下，请你利用本实验的器材提出一个解决办法： ． ④他将钩码重力做的功当作细绳拉力做的功，经多次实验发现拉力做功总是要比小车动能增量大一些．这一情况可能是下列哪些原因造成的（填字母代号）．A．在接通电源的同时释放了小车B．小车释放时离打点计时器太近C．阻力未完全被小车重力沿木板方向的分力平衡掉D．钩码做匀加速运动，钩码重力大于细绳拉力．