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某种型号汽车四个轮胎半径相同,均为R=40cm,同侧前后两轮胎之间的距离(指轮胎中心之间距离)为l=280cm (假定四个轮胎中心构成一个矩形).当该型号汽车开上一段上坡路ABC(如图(1)所示,其中∠ABC=a(
3
4
π<a<π
),且前轮E已在BC段上时,后轮中心在F位置;若前轮中心到达G处时,后轮中心在H处(假定该汽车能顺利驶上该上坡路).设前轮中心在E和G处时与地面的接触点分别为S和T,且BS=60cm,ST=100cm.(其它因素忽略不计)
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    On July 24, 1916, a natural gas explosion trapped 32 men working in a tunnel 250 feet below Lake Erie. The first rescuers who entered the tunnel were 1 by gas, and for hours no one else dared to enter the suffocating (窒息的)2 deathtrap.

    Then, late that night, someone had an idea3 Garrett Morgan and his new invention. Garrett Morgan was a successful 4 owner in Cleveland. The son of freed slaves and the seventh of 11 children, mechanically minded Morgan had opened his own sewing machine shop, which he soon 5 to a tailoring factory with 32 employees.

    In the early 1900s, factory buildings were crowded and untidy. They were often6 of wood, with no fire escapes. Fire could cause serious7 Concerned about his employees, Morgan 8 with a “safety hood” (头罩) that would allow the wearer to9 despite a fire's poisonous smoke.

    Morgan knew smoke rises during a fire10 he created a heat-resistant hood with a long tube reaching to the floor. Wearing Morgan's hood, a firefighter could breathe the 11 air near the 12 Morgan lined the breathing tube with a sponge-like material that was wetted before use to13 the air. A second tube was designed to14 exhaled (呼出的) air.

    Called to the scene on the night of the tunnel explosion, Garrett arrived with samples of his safety hood. Still in their nightwear, he and his brother Frank put on the hoods and 15 entered the tunnel. It was a dangerous 16 of the invention, but they saved two lives and 17four bodies before officials closed the18Morgan knew that more lives might have been saved if he had been called sooner.

    The daring19 made Morgan famous and brought requests for safety hoods from fire departments around the country. But his greatest20 was knowing that his invention would now save more people.