【題目】 “神州二號”無人飛船環(huán)繞地球108圈，順利完成預(yù)定空間科學(xué)試驗任務(wù)后，于2001愿軍年1月16日在內(nèi)蒙古中部準(zhǔn)確返回，成功著陸，標(biāo)志著我國載人航天工程第二次飛行實驗取得圓滿成功，若飛船穿越大氣層時，有一段為勻速降落過程，則在此過程中飛船的（ ）

A．動能減小，機(jī)械能增大 B．動能不變，機(jī)械能減小

C．動能增大，機(jī)械能減小 D．動能減小，機(jī)械能不變

【答案】B

【解析】

試題分析：動能大小的影響因素：物體的質(zhì)量、物體的速度，質(zhì)量越大，速度越大，動能越大；

重力勢能大小的影響因素：物體的質(zhì)量、物體的高度，質(zhì)量越大，所處的位置越高，重力勢能越大；

動能和勢能統(tǒng)稱為機(jī)械能．

解：當(dāng)飛船勻速降落時，飛船的質(zhì)量不變、速度不變，動能不變；飛船的質(zhì)量不變，高度越來越小，重力勢能越來越小，機(jī)械能減�。�

故選B．

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