问题 问答题

从一定高度下落的乒乓球,碰到桌面后又弹起上升到某一高度,在整个过程中能量转化的顺序是:势能-动能-势能______.

答案

乒乓球从一定高度下落时重力势能最大,下落过程中重力势能减小动能变大,刚接触桌面动能减小弹性势能增大;被弹起时弹性势能最大,弹性势能转化成动能乒乓球弹起,在上升过程中,动能减小转化成重力势能.

故答案为:×.

单项选择题
单项选择题

People have good reason to care about the welfare of animals. Ever since the Enlightenment, their treatment has been seen as a measure of mankind’s humanity. It is no coincidence that William Wilberforce and Sir Thomas Foxwell Buxton, two leaders of the movement to abolish the slave trade, helped found the Royal Society for the Prevention of Cruelty to Animals in the 1820s. An increasing number of people go further: mankind has a duty not to cause pain to animals that have the capacity to suffer. Both views have led people gradually to extend treatment once reserved for mankind to other species.

But when everyday lives are measured against such principles, they are fraught with contradictions. Those who would never dream of caging their cats and dogs guzzle bacon and eggs from ghastly factory farms. The abattoir and the cattle truck are secret places safely hidden from the meat-eater’s gaze and the child’s story book. Plenty of people who denounce the fur-trade (much of which is from farmed animals) quite happily wear leather (also from farmed animals).

Perhaps the inconsistency is understandable. After hundreds of years of thinking about it, people cannot agree on a system of rights for each other, so the ground is bound to get shakier still when animals are included. The trouble is that confusion and contradiction open the way to the extremist. And because scientific research is remote from most people’s lives, it is particularly vulnerable to their campaigns.

In fact, science should be the last target, wherever you draw the boundaries of animal welfare. For one thing, there is rarely an alternative to using animals in research. If there were, scientists would grasp it, because animal research is expensive and encircled by regulations. Animal research is also for a higher purpose than a full belly or an elegant outfit. The world needs new medicines and surgical procedures just as it needs the unknowable fruits of pure research.

And science is, by and large, kind to its animals. The couple of million (mainly rats and mice) that die in Britain’s laboratories are far better looked- after and far more humanely killed than the billion or so (mainly chickens ) on Britain’s farms. Indeed, if Darley Oaks makes up its loss of guinea pigs with turkeys or dairy cows, you can be fairly sure animal welfare in Britain has just taken a step backwards.

With which of the following statements would the author most probably agree()

A. Even if they deplore the activitist’s use of intimidation and violence, animal lovers everywhere can sure rejoice today

B. Science does not deserve to be the target of protests, whatever you think of animal rights

C. Over the years something good has come from the campaign against the animal industry

D. It is a sensible move that Darley Oaks makes up its loss of guinea pigs with turkeys or dairy cows