题干

掉在水平地面上的弹性小球会被弹起,而且弹跳的高度会越来越低.图所示是小球弹跳的频闪照片,MN为等高线,小球在3、5位置的高度一样.不计空气阻力,则:(1)小球在图中位置____时的势能最大;(2)小球在位置3和位置5时比较,它们的机械能____(填“相等”或“不相等”)(3)小球从位置____到位置4的过程中,动能转化为势能.

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答案(点此获取答案解析)

1,不相等,3

同类题4

阅读下列短文,从每题所给的A、B、C和D四个选项中,选出最佳选项。

A

San Francisco Fire Engine Tours

San Francisco Winery Tour

   Running: February 1st through April 30th

   This delicious tour goes through the city on its way to Treasure Island where we will stop at the famous Winery SF. Here you can enjoy 4 pours of some of the best wine San Francisco has to offer.(Included in tickets price)

  Departing from the Cannery: Tell time upon request.

  Duration(时长):2 hours

  Price: $90


Back to the Fifties Tour

  Running: August 16th through August 31st

  This tour transports you back in time to one of San Francisco’s most fantastic periods, the 1950s! Enjoy fun history as we take you through San Francisco for a free taste of ice cream.

  Departing form the Cannery 5:00 pm and 7:00 pm

  Duration:2 hours

  Price:$90

Spooky Halloween Tour

  Running: October 10th through October 31st

  Join us for a ride through the historical Presidio district .Authentic fire gear (服装)is provided for your warmth as our entertainers take you to some of the most thrilling parts of San Francisco

  Departing from the Cannery:6:30 pm and 8:30 pm

  Duration :1 hour and 30 minutes

  Price: Available upon request

Holiday Lights Tour

  Running: December 6th through December 23nd

  This tractive four takes you to some of San Francis’s most cheerful holiday scenes. Authentic fire gear is provided for your warmth as you get into the holiday spirit.

  Departing from the Cannery 7:00 pm and 9:00 pm

  Duration: I hour and 30 minutes

  Advance reservations required.