问题 多选题

质量相同的两个物体,分别在地球表面和月球表面以相同的初速度竖直上抛,不计空气阻力,比较这两种情况,下列说法中正确的是(  )

A.物体在地球表面时的惯性比物体在月球表面时的惯性大

B.各自落回抛出点时,重力做功的瞬时功率相等

C.在各自都上升到最高点的过程中,它们的重力做的功相等

D.在空中飞行的过程中,它们的机械能都守恒

答案

A、质量是惯性大小的量度,质量相等,物体在地球表面和月球表面的惯性大小相等.故A错误.

B、物体竖直上抛返回到出发点的速度大小相等,根据P=mgv,知重力大小不等,所以重力做功的瞬时功率不等.故B错误.

C、小球上升到最高点的过程中,根据动能定理知,克服重力做功等于动能的减小量,动能减小量相等,知重力做功相等.故C正确.

D、在空中飞行的过程中,只有重力做功,所以机械能守恒.故D正确.

故选CD.

选择题
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61. We can find this passage in a ________ in a hotel.

A. café bar        B. front-desk    C. fitness center     D. guest room

62.If you forget your comb, you can         .

A. buy one in the hotel shop    B. replace one with a tooth brush

C. phone the front-desk to get one D. go in person and get one at the front desk

63. Leaving the towels on the floor means that        .

A. you want to join in the program B. you want the room-maid to hang it up

C. you need them collected and washed         D. you want to use them more than once

64. What is the Project Planes Program trying to do?

A. Make your bed sheets cleaner.   B. Work for a better environment.

C. Help guests checking out faster.         D. Persuade guests to stay longer.