题干

一洗衣机正常工作时非常平稳,当切断电源后,发现洗衣机先是振动越来越剧烈,然后振动再逐渐减弱,对这一现象,下列说法正确的是
①正常工作时,洗衣机波轮的运转频率比洗衣机的固有频率大
②正常工作时,洗衣机波轮的运转频率比洗衣机的固有频率小
③正常工作时,洗衣机波轮的运转频率等于洗衣机的固有频率
④当洗衣机振动最剧烈时,波轮的运转频率等于洗衣机的固有频率

A:① ④

B:只有①

C:只有③

D:② ④

上一题 下一题 0.0难度 选择题 更新时间:2019-12-16 10:38:36

答案(点此获取答案解析)

A

同类题2

阅读短文,然后根据其内容选择正确答案。

Dear mum and dad,

    I'm writing this letter to you from the center of Australia. At themoment we're staying near Uluru—that's the aboriginal(土著) name for Ayers Rock. On the first day, we took a balloon tour over the rock, and I was surprised at how big it was: 3.6 kilometers long and 384 meters high. The colors of the rock are fantastic, and at different times of the day, they change from purple to red. The Aborigines are the first people of Australia, and the ancient aboriginal stories describe the spirits that created the world. Uluru is a center of Aboriginal culture.

    The Australians have many British relatives. That's why they're like us in many ways. Their family life is similar to ours, and they enjoy the same food and hobbies. The food and drink that most Australians like are grapes, lamb, ham and especially wine that they make in the south of the country. They love all sports, but football is the most popular. Most Australians live near the coast, so they also love going to the beach, swimming and surfing.

Although it's December, it's summer over here. The sunshine is very bright, and near the coast the countryside is very green. There are lots of sheep in the fields and on the hills, but the outback(澳洲内陆) is more like a desert, full of rocks and sand.

    The next day after we arrived at Uluru, we went on a camel(骆驼) ride. The camel that I rode had a bad temper. When I sat on its back, it became very angry and refused me. So everyone else thought it was very funny that my camel kept lying down…

    Finally, later this evening, we're taking the plane back to Sydney and coming home, it's been a fantastic trip!

Tony