坐第排球是国际残疾人比赛项目之一,主要是为下肢有残疾的人而设的项目。
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一物体悬挂在弹簧下方作简谐振动,当这物块的位移等于振幅的一半时,其动能是总能量的_____________。
A. 1/4
B. 1/3
C. 1/2
D. 3/4
当一平面简谐机械波在弹性媒质中传播时,下述各结论哪个是正确的?
A. 媒质质元的振动动能增大时,其弹性势能减小,总机械能守恒。
B. 媒质质元的振动动能和弹性势能都作周期性变化,但二者的位相不相同。
C. 媒质质元的振动动能和弹性势能的位相在任一时刻都相同,但二者的数值不相等。
D. 媒质质元在其平衡位置处弹性势能最大。
It seems somewhat ________ to expect anyone to drive 3 hours just for a 20-minute meeting.
A eccentric
B impossible
C absurd
D unique
This area of the park has been specially ________ for children, but accompanying adults are also welcome.
A inaugurated
B designated
C entitled
D delegated