(Ⅰ)求证:B1F⊥平面AEF;
(Ⅱ)求三棱锥E﹣AB1F的体积.
由∠BAC=90°,且AB=AA1=1,得 B1F=6
质量为20kg、底面积100cm2的物体静止在水平地面上,用如图所示的滑轮组在5s内将物体匀速竖直提升3m,已知动滑轮重50N,不计绳重和摩擦.(g=10N/kg),求:
Lucy doesn't feel l____because she has many friends.
加稀盐酸的次数
1
2
3
4
5
加稀盐酸的质量/g
20
剩余固体的质量/g
16.75
13.5
10.25
7