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【简答题】
一辆小汽车正在匀速爬上六盘山一是1 000 m、坡高h是60 m的盘山路，小汽车的质量m是1 000 kg，小汽车的牵引力F是720 N．（计算结果保留两位小数） （1）如图所示，上山的路修成盘山弯曲的，目的是________． （2）如果小汽车上坡所用时间为60 s，求汽车牵引力做功的功率是多大？ （3）这段盘山路的机械效率是多少？（取g＝10 N/kg）
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