If you cut one in the center of the board

1. Gravity is related to mass, so if one piece is g out, the mass will decrease and the gravity will decrease< Br > for an object with regular shape and uniform mass distribution, the center of gravity is at its geometric center. For a circular homogeneous thin plate, if a small circle is g out to form a ring with the center of the plate as the center, it is still an object with regular shape and uniform mass distribution, so the center is still at the center of the plate, so the center of gravity remains unchanged; Option C is correct and abd is wrong. < br > so select: C

2. Well, if the middle part of the plate is g out, the mass of the plate is reced compared with the previous one, and the gravity is also reced; Because what is g out is a wish, so the center of gravity is still in the central position, so it remains unchanged.

3. A cube, if a small cube is g out at the center of a surface, then the surface area is larger than the original

4. In fact, the excavated part is equivalent to 6 cuboids + 1 cube. The edge of the cuboid is 2,2,3, and the cube is 2,2,2
so the volume is 8 & # 179- 6*2²* 3-2³= 432
surface area, the extra part after digging out is the side area of six cuboids, each side area is 2 * 3, there are four sides, that is 2 * 3 * 4, there are six cuboids, so it is 2 * 3 * 4 * 6, at the same time, there is a 2 * 2 square area on each side, a total of six, 6 * 2 * 2
so the surface area is 8 * 8 * 6-6 * 2 * 2 + 2 * 3 * 4 * 6 = 504

5. 40x30 = 1 piece of wood
40 length - the length of the cut 20, according to the center of the cut, there should be 10 length
30 width, the height of the cut U-shaped hole is 15, the so-called height is the width, the height of 30 minus 15
40x30 a piece of wood, the area of the cut wood should be 20 length, 15 width
20X15 is all the area of the cut 40x30

6. If you think about it, the cube has six faces. The surface area of the cube in this question is only two faces, and there are still four faces left. So there are two more faces. I mean the face of the small cube

7. I don't know which one you're learning.
for example, the oil jacket in the wood board has out of print color, which is to prepare the wood board, ink, cutting knife (round knife, oblique knife, triangular knife, flat knife... More tools, more convenient), brush, milky glue, roller (one big and one small), shovel (shovel ink, color adjustment), cardboard, sandpaper (coarse sand, fine sand), etc Copy paper, paper, tool knife, ruler, pencil, line marker, car washing water (used to clean the ink on the board) and copper plate machine (used to press out the picture effect) the proction process is as follows: 1. First cut the board, then polish it with sandpaper, and brush a layer of milky white glue (to prevent the board from cracking) 2. Copy your sketch with paper, and pad the carbon paper on the board, Lay the reverse side of the paper on the board, it well and trace it with a line marker to prevent the screen from being washed out when washing the ink. 3. Start to be stereotyped. Carve out the picture you want to print first, then wash off the ink and wipe it clean with a rag. It's better to print bright color first and then black. If you want to challenge, you can print black first. If the picture has lemon yellow and rose red, it's better to print it first, because it's not easy to cover In fact, it's not easy to say. When we started learning, we had to see the teacher do it before we knew it)
watermark Prints: Jiaxuan, Malian, shading pen, large color mixing box, laminated scales (just like plastic paper), printing method is similar to oil jacket, mainly because the effect is very different, watermark is very difficult, not very easy to master
silk screen printing: I'm not very familiar with it. I'll learn it next semester. I'm sorry

9. Because it is hollowed out, there are only five surfaces, minus the original one, the increased surface area of each large surface is: 1 * 1 * 4 = 4 square centimeter, the total increased surface area of six surfaces is 6 * 4 = 24 square centimeter
the original surface area is 6 * 4 * 4 = 96 square centimeter
the total surface area is 96 + 24 = 120 square centimeter