问题 填空题

小明质量为50kg,站在水平地面上,双脚与地面的接触面积为500cm2,小明对地面的压强为         __________Pa,若小明用300N的力竖直向上提静止在地面上重力为800N的物体,则物体所受合力为      N(g=l0N/kg)。

答案

1.0×104;0。

小明对地面的压力为F=G=mg=500N,故小明对地面的压强p==1.0×104Pa。小明提物体时,没提起来,说明物体仍处于静止状态,由平衡力的知识,故它受到的合力为零。

问答题
单项选择题

Are you interested in seeing the beautiful fall foliage of New England but tired of traffic jams and overbooked hotels Then this year forget the crowds in New England and see the beautiful colors of autumn in the Catskills.

These rugged mountains in New York State, just 90 miles northwest of New York City, are famous for the legendary tales of Rip Van Winkle, and more recently for the summer hotels mat sprang up in the region during the 1940s, 1950s, and 1960s. Families trying to escape the heat of New York City found the Catskills to be the perfect place to stay for a month or so each summer. By the late 1950s there were over 500 resorts and hotels offering nighttime entertainment as well as all kinds of outdoor activities. Famous comedies like Jackie Gleason, Joan Rivers, and Sid Caesar all got their start touring the hotel clubs here. Since the introduction of air-conditioning and cheaper air travel, however, families have stopped coming to the Catskills in such large numbers, chasing instead more distant locations at different times of the year. Many of the Catskills hotels closed in the 1970s, but some remain and have expanded and changed their facilities to meet the needs of today’s visitors.

Currently, there are many activities available to the traveler besides witnessing the changing colors of the leaves. There is an all-organic sheep farm where visitors can see how a traditional sheep farm operates. There are also hundreds of miles of scenic drives in the area. Route 42, for instance, is an excellent site for spotting bald eagles. For more information on vacations in the Catskills, call the office of Public Information.

According to the passage, the decline in the number of resorts in the 1970s was caused by ().

A. television

B. shorter vacations

C. affordable air travel

D. more traffic