题干

随着人们生活水平的逐渐提高,小轿车已经走进了千家万户.前不久,小明家也新买回来了一辆小汽车,好奇的小明找出了小汽车如下表列出的有关数据:(g=10N/kg,1L=103m3

小汽车的质量1200kg

小汽车的额定功率90kW

每个轮胎与地面的接触面积500cm2

100km耗油量10L

汽油的密度0.71×103kg/m3

汽油的价格6.25元/L

求:(1)该小汽车静止在水平地面上时,对地面的压强是多大?

(2)若该小汽车行驶100km,则需耗油多少千克?

(3)小明发现该小汽车在水平路面上以额定功率匀速运动的速度是72km/h,请计算该车行驶100km牵引力所做的功.

(4)假如小明还想知道小汽车发动机正常工作时的效率大约是多少,则小明还需查阅的信息有哪些?

上一题 下一题 0.0难度 选择题 更新时间:2019-10-24 10:36:56

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解:(1)该小汽车静止在水平地面上时,对地面的压强:p=FS=GS=mgS=120

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    Skateboarding is an action sport which includes riding and performing tricks using a skateboard, as well as an activity for fun, an art form, an entertainment industry job, and a method of transportation. In 2016, it was announced that skateboarding will be represented at the 2020 Summer Olympics in Tokyo, Japan.

    There are various theories about the origins of Skateboarding, but it is generally held that the sport began in the 1940s on the west coast of the USA when metal wheels were attached to a narrow wooden board. In the 1950s, plastic replaced metal as the material of choice for the wheels, and the first "Roller Surfboard" become commercially available, which in turn developed into the skateboard that we know today. The sport was a big hit with the younger generation and grew in global popularity in the 1980s and 1990s. Since the late 1990s, skateboarding has become an important part of street culture.

    However, skateboarding has raised heated discussions in areas where the activity, although legal (合法的), has damaged stone works, steps, benches, and parks. Certain cities oppose the building of skate parks in their neighborhoods, for fear of increased crime (犯罪) and drugs in the area. The disagreement between the old image of skateboarding and a newer one is quite obvious: magazines such as Thrasher describe skateboarding as dirty, and still firmly tied to punk (朋克), while other publications, Transworld Skateboarding as an example, paint a more different and controlled picture of skateboarding. As more professional skaters use hip hop, or hard rock music in their videos, many urban youths, hip-hop fans and hard rock fans are also drawn to skateboarding, weakening the sport's punk image. Besides, group spirit influences the members of this community. In presentations of skateboarding, the evidence of crime is absent, and no attempt is made to tie extreme sports to any kind of illegal activity.

    The good news is that efforts have been made to improve recognition of the cultural heritage as well as positive effects of skateboarding in cities. By raising £790,000, the Long Live Southbank initiative managed to stop the destruction of a forty years old spot in London due to urban planning, a rescuing operation whose effect extends beyond skateboarding. The presence of skateboarders on this public space keeps the area under nearly constant watch and drives homeless people away, increasing the feeling of safety in the area. The activity attracts artists such as photographers and film makers, as well as a significant number of tourists, which in turn drives economic activity in the neighborhood.