如图所示,长为l的细绳一端固定,另一端拴质量为m的小球,将小球拉至水平位置后由静止释放,则小球摆到最低点速度为________,此时细绳对小球拉力为________。
,3mg
一块质量是27g,体积是10cm3的金属的密度是多少g/cm3?
Why did the United States first launch satellites into space
A.To improve navigation for warplanes and warships.
B.To guide smart bombs that home in on moving targets.
C.To collect meteorological data.
D.To sense remote volcanic eruptions.