问题 选择题

在平坦的垒球运动场上,击球手将垒球水平击出,垒球飞行一段时间后落地.若不计空气阻力,则垒球(  )

A.落地前,垒球做匀变速直线运动

B.落地前,垒球做变加速曲线运动

C.落地前,垒球的速度变化方向竖直向下

D.落地时,垒球的速度方向与水平地面可能垂直

答案

A、击球手将垒球水平击出,垒球飞行一段时间后落地,垒球有水平初速度,仅受重力,做匀变速曲线运动.故A、B错误.

C、因为平抛运动的加速度方向竖直向下,则速度变化量的方向始终竖直向下.故C正确.

D、因为平抛运动在水平方向上做匀速直线运动,竖直方向上做自由落体运动,落地时的速度等于水平分速度和竖直分速度的合速度,根据平行四边形定则知,落地的速度不可能与地面垂直.故D错误.

故选C.

单项选择题

The Supreme Court will hear arguments about the use of public money for the private schooling of children with special needs. It’s interesting to note what’s not at issue: namely, that when a public school system is unable to provide an appropriate education, it is obligated to pay the costs of private school. Too bad poor children don’t have that unshakable right; if they did, there would be no controversy about the District program that gives vouchers to low-income children to attend private schools.

The case to be heard by the court hinges on whether parents have to enroll a child with special needs in public school before the child can attend private school at public expense. Special-education advocates say students shouldn’t have to waste time before being placed in a setting that best suits their needs, while school boards worry about a ruling that could amount to an unfettered fight to private schooling at public expense. What strikes us about the emotionally charged debate is the acceptance by both sides that sometimes it is appropriate to use public money to pay for a child to go to a private school. So, why all the arguments about the approximately$14 million for a federally funded program that lets 1,700 D. C. students attend private schools instead of failing public schools

To hear critics of the D. C. Opportunity Scholarship Program tell it, the use of public money for private schooling is as unprecedented as it is undesirable. In addition to the billions of dollars spent annually on private school tuitions for students with disabilities, private schools get public money for books, technology and teacher training. As long as the money is seen as benefiting the child, it is considered a proper, even desirable, use of public dollars.

Don’t get us wrong. We’re not arguing for the unilateral right of parents to enroll their sons and daughters in any school they wish with the taxpayers picking up the bill. Abuse of special-education policies has contributed to increased costs that threaten to take needed money from general public education funds. Safeguards are needed. Public schools should be pressed to do a better job for students with disabilities and students without. But there are schools in Washington where statistics show that failure is almost guaranteed. If a school system can’t educate a child—whether because of acute special needs or its own historical failings—why should that child not have options for a " free appropriate public education "

Which of the following is TRUE about the special-education advocates’ opinion()

A. They ply believe that children should be put directly into the private schools

B.They think that children should try out both places before making decisions

C. They don’t feel there is still a need to argue about this problem any more

D. They hold the opinion that parents can make decisions for their children

名词解释