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如图，已知斜面倾角300，物体A质量mA=0.4kg，物体B质量mB=0.7kg，H=0.5m．B从静止开始和A一起运动，B落地时速度v=2m/s．若g取10m/s2，绳的质量及绳的摩擦不计，求：

（1）物体与斜面间的动摩擦因数

（2）物体沿足够长的斜面滑动的最大距离．

答案

（1）以AB组成的整体为研究对象，根据动能定理得：

mBgH-mAgsinθ?H-μmAgcosθ?H=

1
2
(mA+mB)v2

得：μ=

(mB-mAsinθ)gH-
1
2
(mA+mB)v2
mAgcosθ

代入解得：μ=

3
10

（2）设物体沿斜面滑动的最大距离为S，根据动能定理得

B落地后过程，对A：

-mAgsinθ?（S-H）-μmAgcosθ（S-H）=0-

1
2
mAv2

代入解得，S≈0.8m

答：

（1）物体与斜面间的动摩擦因数为μ=

3
10
．

（2）物体沿足够长的斜面滑动的最大距离为0.8m．

单项选择题

栓剂的常用基质可可豆脂的熔点是（）

A.20℃～25℃

B.25℃～30℃

C.30℃～35℃

D.35℃～40℃

E.40℃～45℃
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填空题

Recycling Paper


The process of recycling paper can help to reduce deforestation and energy consumption on a significant scale. There are many different reasons why we should recycle paper products, and some of these are (26) in the paragraphs below.
Energy consumption will always be on the (27) as population levels grow, and so any manufacturing processes which help to reduce energy consumption are (28)
The Energy Information Administration (EIA) claim that there can be as (29) as a 40% energy saving when recycling paper over producing paper (30) the direct raw material.
Although recycling paper has many (31) , it also has its drawbacks. One of these drawbacks is that we cannot recycle the (32) paper product for eternity, as the fibers contained within the paper degrade over time, (33) their strength and length.
On (34) , an individual paper fiber can only be recycled a (35) of six times. Although this is a significant drawback, the six time recycling process will help to (36) a great deal of energy when you consider (37) much paper there is to be recycled.
If paper fibers can be recycled up to 6 times, and we recycled all paper products, this could help to (38) the intensity of deforestation for paper products up to a factor of 6.
With paper production said to (39) around 40% of harvested wood, and paper said to (40) around 90% wood, you can see how recycling paper is an important process for the (41) of our forests.
Today, the use of recycled paper products is on the increase, as more and more people begin to recycle paper (42) products around the home.
Although there are slight differences in the recycling processes of different (43) of paper products (e.g. corrugated, mixed paper, newspaper products), we are able to recycle just about any type of paper product around today.
The recycling logo helps to (44) a recyclable product and can also sometimes help to identify if the product contains any recycled material, in the form of a percentage. This helps a consumer to identify the (45) of recycling various products.

A. chances B. applicationsC. benefits D. risks
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