题干

一木块在0.5N的水平拉力作用下,在水平桌面上沿拉力方向做匀速直线运动,若把拉力增大到0.8N,仍使木块在该平面上运动,这时木块受到的摩擦力为____N。如图所示为一种浴室防滑踏垫,其正面为仿草坪式设计,这是通过____的方法增大脚与垫之间的摩擦力;与地板接触的反面有许多小吸盘,利用____将吸盘挤压到地面后,可达到防滑效果。

上一题 下一题 0.0难度 选择题 更新时间:2018-10-27 11:21:42

答案(点此获取答案解析)

0.5,增大接触面的粗糙程度,大气压

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    For the first time in the history of the Beijing, Shanghai and Hangzhou marathons, fourteen blind runners competed in the Nov 6 Hangzhou Marathon this year with the assistance of personal guides. Each runner was supported by 4 or 5 volunteers. Among them was Yan Wei, from a running group called “Running in the Dark”, which specially provides training for blind runners.

    During trainings, blind runners are each accompanied by three volunteers. One volunteer is responsible for removing any obstacles(障碍物)on the road and controlling the pace. The second volunteer acts as a lookout for other runners or vehicles on the path while the third, who is attached to the blind runner by a safety rope, takes note of the trainee's running gait and pace.

    Zhu Peihua, the leader of the group's Shanghai branch, first developed a passion for running last year when he took part in a guided running activity. Zhu said that he was so fascinated with the sport that he even bought a treadmill(跑步机)so that he could train at home. “Running gives me the chance to be outside and take in the fresh air. The activity has also made me more willing to talk to people. It's simply good for health, ” said Zhu.

    The popularity of guided running activities for blind people has been growing since last year. Cheng Yi, a volunteer at Running in the Dark's Hangzhou branch, said that both the numbers of blind runners and volunteers to become assistants to them are rising continually. However, he added that volunteers face a more physically demanding task compared to a regular runner. Some of the other challenges involve being aware of the verbal(口头的) instructions one gives.

     “At the beginning, I kept saying ‘here' and ‘there' instead of ‘left' or 'right' which is much more specific and relevant to the runner. A blind runner once collided with another runner because of my mistake. Luckily, no one was hurt,” said Cheng. Through everything, according to Cheng, he and many of the blind runners he has guided become close friends with shared topics and increased understandings.