题干

下列运动过程中,机械能一定守恒的是(   )

A:做自由落体运动的小球

B:在竖直平面内做匀速圆周运动的物体

C:在粗糙斜面上匀加速下滑的物块

D:匀速下落的跳伞运动员

上一题 下一题 0.0难度 选择题 更新时间:2015-03-24 03:15:27

答案(点此获取答案解析)

A

同类题2

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    Welcome to Orlando! It has a host of attractions and activities. Ready to join the party and plan a visit to O-Town? Just print out our list that suits your style.

    Universal Orlando's Islands of Adventure

    The addition of The Wizarding World of Harry Potter was among the list of must-visits for theme park enthusiasts. Each of the park's “islands” — Toon Lagoon, Jurassic Park, and The Lost Continent — has unique appeal in the form of rides and interactive attractions. (407-363-8000)

    Gatorland

    It bills itself as “Orlando's best half-day attraction”, for in a city people are limited by their time and money. Catch Gatorland's animals and handler(驯化) shows in the afternoon. There's a nighttime run as well, including the Gator Night Shine and various activities. Gatorland ranks as a comparative theme-park bargain. (407-855-5496)

    Aquatica

    One of the city's most unique water parks, Aquatica is a fantastical world of twisting, turning rides and sparkling white sand beaches. And if you enjoy a side of terror with your water-park fun, be sure to check out Ihu's Breakaway Falls. This towering slide is an eight-story mind-bender of a plummet(垂直落下) that is not for the weak heart. The less exciting will still find plenty of fun splashing from one giant wave pool to another or drifting down the lazy river through a world of unusual fish. You can also watch the black-and-white Commerson's dolphins underwater. (407-351-3600)

    Warbird Adventures

    Few attractions are more hands-on historic than Warbird Adventures, which offers thrill-seekers the opportunity to fly like the hero aces of World War II in the North American T-6 Texan. Flights range from 15 minutes to an hour. A visit to the nearby Kissimmee Air Museum is a wonderful way to round out the experience. (407-870-7366)

同类题4

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     I was very disappointed not to be able to go to the jazz concert last Friday. The advertisement in the paper said that you could buy tickets at the theatre box in Richland Hills any day between 10:00 and 4:00. Since I work from 9:00 to 5:30, the only time I could go to the theatre was during my 45-minute lunch break.

    Unfortunately, the theatre is on theother side of the town, and the bus service between my office and Richland Hills is not very good. Butif you are lucky, you can make the round trip in 45 minutes. Last Monday, Istood at the bus stop for 15 minutes waiting for the bus, By the time I saw onecome around the corner, there was not enough time left to make the trip.

     So I gave up and went back to the office. The same thing happened on Tuesday, and again next day. On Thursday, my luck changed. I got on a bus right away and arrived at the theatre in exactly 20 minutes. When I got there, however, I found along line of people at the box office, I heard one man say he had been waitingin line for over an hour. Realizing I would not have enough timeto wait in line. I caught the next bus and headed back across the town.

    By Friday I realized my only hope was tomake the trip by taxi, it was expensive, but I felt it would be worth it tohear the concert. The trip by taxi only took 10 minutes, but felt like an hour to me. When I got to the theatre, I was relieved to see that nobody was waiting in line. The reason, however, I quickly discovered, was that they had already sold all the tickets.