甲、乙两运动员在训练交接棒的过程中发现:甲经短距离加速后能保持9m/s的速度跑完

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问题:

甲、乙两运动员在训练交接棒的过程中发现:甲经短距离加速后能保持9m/s的速度跑完全程;乙从起跑后到接棒前的运动是匀加速的.为了确定乙起跑的时机,需在接力区前适当的位置设置标记.在某次练习中,甲在接力区前S0=13.5m处作了标记,并以V=9m/s的速度跑到此标记时向乙发出起跑口令.乙在接力区的前端听到口令时起跑,并恰好在速度达到与甲相同时被甲追上,完成交接棒.已知接力区的长度为L=20m.

求:(1)此次练习中乙在接棒前运动的时间t;

(2)此次练习中乙在接棒前的加速度a;

(3)在完成交接棒时乙离接力区末端的距离△S.

考点:匀变速直线运动的位移与时间的关系匀变速直线运动的位移与速度的关系
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砌筑墙体中,可以不设置过梁的洞口最大宽度为()

A.250mm

B.300mm

C.400mm

D.500mm

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The Antarctic is actually a desert. It’s the only continent on the earth without a river or lake.

The Antarctic is all ice all year round. The warmest temperature ever recorded there is zero, at the South Pole. Explorers used to think that a place so cold would have a heavy snowfall. But less than ten inches of snow falls each year. That is less than half an inch of water. The times that much water falls in parts of the Sahara.

The little snow that falls never melts. It continues to pile up deeper and deeper year after year and century after century. When the snow gets to be about 80 feet deep it is turned to ice by the weight of the snow above it.

1. Antarctic is called a desert because it _______.

A. is sandy       B. is cold       C. has little water     D. is high

2. The snow there is very deep because it _______.

A. never stop falling          B. piles up year after year

C. never melts               D. falls often

3. The best title for the passage is ______.

A. Waterfall at the South Pole        B. The Antarctic ------An Ice Desert

C. Snowfall at the South Pole        D. The world’s Great Desert

题型:问答题

通过发行股票筹资,可以不支付利息,因此其成本比借款筹资的成本低。 ( )

题型:问答题

霍尔发生器位于传感器()之中。

A、原边回路

B、磁路的气隙

C、电子电路

D、次边线圈

题型:问答题

鸦片战争后签定了中英《南京条约》,在该条约的各项条款中,最能体现英国发动战争的本质意图的是()

A.割占香港岛

B.赔款2100万银元

C.领事裁判权

D.五口通商

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