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【題目】我國發(fā)射的宇宙飛船在完成任務后，返回地面指定地點，宇宙飛船在下落到地面附近時，由于空氣阻力作用做勻速直線運動，則宇宙飛船在勻速下降的過程中，它的（�。�

A.動能不變，勢能減小，內能增大　　　

B.動能不變，勢能增大，內能減小

C.動能減小，勢能不變，內能增大　　　

D.動能增大，勢能減小，內能不變

【答案】A

【解析】試題分析: 我國發(fā)射的宇宙飛船在完成任務后，返回地面指定地點，宇宙飛船在下落到地面附近時，由于空氣阻力作用做勻速直線運動，則宇宙飛船在勻速下降的過程中，由于它是勻速運動的所以，動能是不變的。飛船的高度在減小，所以勢能變小。飛船和空氣有摩擦，在下落的過程中機械能會轉化為內能。

A.動能不變，勢能減小，內能增大　　　符合題意；

B.動能不變，勢能增大，內能減小 不合題意；

C.動能減小，勢能不變，內能增大　　　不合題意；

D.動能增大，勢能減小，內能不變 不合題意；

故選A。

考點:本試題考查的是機械能的轉化。動能是物體由于運動而具有的能量，動能跟物體的質量和物體運動的速度有關。勢能跟物體的質量和物體被提升的高度有關。

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