题干

人们对电动自行车褒贬不一.其轻便、环保的优点受消费者欢迎,但电池的持续耐用性又令人感到不足.小明购买了一台某型号电动自行车,主要技术参数如表所示.请回答下列问题:(取g=10N/kg)

无刷电机

48V,400W

整车质量

80kg

(1)小明的质量为60kg,他受到重力为多大?

(2)小明骑上电动自行车行驶时,两轮胎与地面的总接触面积为1.0×10﹣2m2,那么此车对地面的压强多大?

(3)在某平直路段上,电动自行车若以额定功率匀速行驶时,受到的平均阻力为40N,行驶速度为5m/s.则60s内电机对自行车所做的功是多少?电动自行车效率是多少?

(4)如果电池报废后随便扔掉,有什么危害?(请具体说明,一条即可)

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答案(点此获取答案解析)

解:(1)小明受到的重力为G=mg=60kg×10N/kg=600N;(2)电动车的重力为G车=m车g=80kg×10N/kg=800N;行驶的时候电动车对地面的压力F压=G+G车=600N+800N=1400N;对地面的压强P=

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完形填空

    A girl complained to her father about her hard life. She didn't know what she had to do and wanted to1up. She felt tired of fighting and fighting. One problem had been finished but2came over.

    Her father, a cook, took her into the3.He poured water into three pans (锅) and boiled it. When the water was boiling, in the first pan he put some carrots, in the second he put some eggs and in the last he put some coffee. He 4for them for a few minutes without any words.

    The girl waited impatiently, not knowing5her father was doing that. About 20 minutes later, her father turned6the stove, took out the carrots and put them in a bowl. He took out the7and put them in another bowl. After that the coffee was poured into a cup. Turning back to his daughter, he asked, “My sweet heart, what do you8?” “Carrots, eggs and coffee,” she answered.

    Her father told her to 9her eyes and let her touch the carrots. She did so and felt that the carrots were10. After that he asked her to take eggs and11them. Then, she got the eggs, warm and hard. At last, the father asked her to smell the coffee. She asked, “What did you do this for, Father?” He12that each one had had the same unlucky experience—the boiling water, but13had a different result. The strong and hard carrots had become soft and weak after being in the boiling water. The eggs became hard after being cooked. The coffee was very14and it changed the water. “Who are you?” asked her father, “When bad luck15your door, what's your decision? Are you carrots, eggs or coffee?”