题干

气球以20m/s的速度沿竖直方向匀速上升,当它上升到离地160m的高处时,一重物从气球上掉落,则重物需要经过多长时间才能落到地面?到达地面时的速度是多大?(g取10m/s2,不计空气阻力)

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答案(点此获取答案解析)

解:取全过程为一整体进行研究,从重物自气球上掉落开始计时,经时间t落地,规定初速度方向为正方向,画出运动草图,如图所示.
重物在时间t内的位移h=﹣160m,
将h=﹣160 m,v0=20 m/s代入位移公式h=v0t﹣
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    For kids and many adults,a San Diego vacation means theme parks and other attractions.Before heading to a park,call or check its website for updated hours of operation; many parks have seasonal or holiday hours.Ticket prices listed here are for general admission(入场费),single-day use only.

Sea World San Diego

    A 6-minute ride called Journey to Atlantis,which is to open in late May,tells the legend of the island nation. After the ride of Greek fishing boats,folks can visit a new exhibit of dolphins,which have not been on display at the park since 1998.

    DETAILS: General admission is $46.95 for adults,$37.95 for children aged 3-9,free for children 2 and younger. 1-800-380-3203 or www.seaworld.com.

San Diego Zoo

    There's not much in the way of new attractions.The zoo has a new panda cub(幼兽),Mei Sheng.Nighttime Zoo, a program popular with families,starts June 26.

    DETAILS: General admission is $21 for adults,$14 for children aged 3-11,free for children 2 and younger. 1-619-234-3153 or www.Sandiegozoo.com

Maritime(海的)Museum of San Diego

    The HMS Surprise,the 18th-century British warship featured in the film Master and Commander,is on exhibit through Nov.30.

    DETAILS: The ship is available for tours from 9 am to 8 pm daily.Admission is $8 for adults,$6 for seniors and children aged 13-17,$5 for kids aged 6-12,and free for kids 5 and younger.1-619-234-9153 or www.sdmaritime.org.

Old Town Trolley Tours

    Visiting relatives or friends in San Diego? They can get a hometown pass and ride for free with your paid admission.

    DETAILS: The main ticket booth(售票亭)is in Old Town at 4010 Twiggs St.Hours are from 9 am to 5 pm, daily $25.www.historictours.com.