如下图为一机械横波在某时刻的波形图(实线),已知波沿x轴正方向传播,波速为1m/

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问题:

如下图为一机械横波在某时刻的波形图(实线),已知波沿x轴正方向传播,波速为1m/s,经过一段时间Δt后,波形变为图中的虚线所示,则Δt的可能值为

A.1 s

B.3 s

C.5 s

D.7 s

 

考点:波长、频率和波速
题型:选择题

(66) is used to ensure the confidentiality, integrity and authenticity of the two end points in the private network. (67) , an application-layer protocol, authenticates each peer in an IPsec transaction. IKE negotiates security policy, determining which algorithm may be used to set up the tunnel. It also handles the exchange of session keys used for that one transaction.
Networks that use (68) to secure data traffic can automatically authenticate devices by using (69) , which verify the identities of the two users who are sending information back and forth. IPsec can be ideal way to secure data in large networks that require secure connections among many devices.
Users deploying IPsec can (70) their network infrastructure without affecting the applications on individual computer. The protocol suite is available as a software-only upgrade to the network infrastructure. This alows security to be implemented without costly changes to each computer. Most important, IPsec allows interoperability among different network devices, PCs and other computing systems.

A.characteristics

B.associated links

C.digital certificates

D.attributes

题型:选择题

水环式真空泵停车顺序正确的是().

A、停电机、关闭工作液体供给管线上阀门、关闭泵出入口阀

B、关闭泵出入口阀、停电机、关闭工作液体供给管线上阀门

C、关闭工作液体供给管线上阀门、停电机、关闭泵出入口阀

D、关闭工作液体供给管线上阀门、关闭泵出入口阀、停电机

题型:选择题

下列计算正确的是(  )

A.a+a2=2a2

B.a5•a2=a10

C.(-2a44=16a8

D.(a-12=a-2

题型:选择题

一位质量m=60kg的滑雪运动员从高h=10m的斜坡自由下滑。如果运动员在下滑过程中受到的阻力大小F=50N,斜坡的倾角θ=30°,运动员滑至坡底的过程中,下列说法正确的是(g取10m/s2) [ ]

A.重力做功6000J  

B.阻力做功1000J    

C.合外力做功7000J    

D.支持力不做功

题型:选择题

出生4~6个月的婴儿需开始补充()

A.铁

B.钙

C.淀粉

D.脂肪

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