Find a board about 1m long, put the board on the horizontal desktop, and pad a few round pencils under it, so that the friction between the board and the desktop is as small as possible What will happen if you find a toy car with batteries and drive it on the board?

The board moved back while the car remained in place

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1. As shown in the figure, in the experiment of studying friction, a small wooden block placed on the horizontal table is pulled horizontally with a spring scale each time, and the reading of the small wooden block's movement is shown in the following table (the contact surface between the wooden block and the table is the same each time): then from the table, we can see () & nbsp; the number of experiments, the movement state of the small wooden block, and the reading of the spring scale (n) 1 static 0.4 2 static 0.6 3 Acceleration 0.7 4 constant speed 0.5 5 deceleration 0.3 A. The maximum friction force on the block is 0.7nb. The maximum static friction force on the block may be 0.5nc. In the five experiments, the friction force on the block is the same three times. D. in the five experiments, the friction force on the block is the same two times
2. When exploring the relationship between acceleration, force and mass, why should we balance the friction, and why can we balance the friction by raising one end of the board
3. As shown in the figure, under the action of horizontal thrust F, the object a moves to the position in figure a at a constant speed. In this process, the pressure of a on the table will decrease, and the pressure of a on the table will decrease The pressure on the table will increase
4. Use the horizontal force F to pull the board a to move to the right on the horizontal table top. When the board a moves from the position shown in the figure to one third of its length and stretches out of the table top, the pressure and pressure of board a on the table top is () A. Pressure unchanged B. pressure decreased C. pressure decreased D. pressure increased
5. The distance between the two trains is D, and they are running at the speed of V1 and V2. There is a carrier pigeon flying at the speed of V3 between the two trains. When the pigeon meets train a at the speed of V3, it immediately turns around and flies to train B, and when it meets train B, it immediately turns around and flies to train A. so when the distance between the two trains is D, it becomes zero. How many distances has the pigeon flown?
6. What is it? It describes how fast an object moves. I checked Baidu Encyclopedia, and he also refers to speed In addition, to describe the acceleration, does the large speed = the fast change of the object motion?
7. Pull an object with force F to make it move in a straight line with uniform acceleration on the horizontal plane with acceleration a. the horizontal component of force F is F1, as shown in the figure. If the force F & cent; with the same size and direction as F1 is used to pull the object instead of F to produce acceleration a & cent;, then: (b c) A. When the horizontal plane is smooth, a & cent; < a B. when the horizontal plane is smooth, a & cent; = a C. When the horizontal plane is rough, a & cent; < a D. when the horizontal plane is rough, a & cent; = a D Please explain why when the plane is smooth, a is the same. F1 is obviously less than f, so its horizontal component is also less than f's horizontal component?
8. What is the average speed of the 100 meter race when the athlete reaches the end of the 10th second and reaches the end of the third second at 8m / s and 13m / S?
9. Description of the speed of the movement ----- speed] requires detailed steps! 1. A particle is on the x-axis and always moves in the positive direction of the x-axis. The position coordinates of each moment are shown in the table below t/s 0 2 4 6 8 10 12 14 16 18 x/m 2 4 6 8 8 8 12 16 20 24 (1) What is the displacement and distance of the particle in the first 10 seconds? (2) What is the instantaneous velocity of the particle at the end of 8s? (3) What is the average velocity of a particle between 0 and 18 seconds? 2. The speed of signal transmission along animal nerve is about 100 m / s. how long does it take for a 30 m whale to feel a bite from a shark on its tail? How long does it take for a 8 m whale to feel a bite from a mosquito on its foot?
10. Physics in grade one of senior high school: description of speed of motion -- speed The average velocity of an object passing through two consecutive equal displacements is V1 and V2 respectively, and the average velocity in the whole process is v = 12m / s. given V1 = 10m / s, the size of V2 can be calculated Give the operation process, thank you!
11. Zhang Jun students in "explore the size of friction more which factors." In the experiment of "exploring which factors are related to the size of friction force", Zhang Jun adopted the following experimental methods: put the long board on the horizontal table, and the wood (2) does the long board have to move in a uniform and straight line in the experiment I'm sorry I can't upload the picture, but please make sure to analyze it for me
12. As shown in the figure, when the board with length of L = 2M and mass of M = 8kg is placed on the horizontal ground, and the speed of the board moving to the right is v = 6m / s, a small block with mass of M = 2kg regardless of size is gently placed at the front end of the board. The dynamic friction coefficient between the board and the ground and between the block and the board is μ = 0.2, g = 10m / S2 (1) The acceleration of the block and the board; (2) the speed of the block sliding away from the board
13. After a polygon cuts an angle from a vertex, the sum of the inner angles of the new polygon is 2520 degrees
14. The original price of a washing machine is 1450 yuan. Now it is sold at a 20% discount, but the price is still higher than the cost. 19. How much is the cost of this washing machine?
15. (1.29+1.37+1.45+.+1.85)/(1.47+2*0.84)≈（） Remember: keep two decimal places!
16. During the promotion period of a shopping mall, it is stipulated that all goods in the shopping mall are sold at 80% of the price. At the same time, when customers spend a certain amount of money in the shopping mall, they can get the corresponding amount of lottery tickets according to the following scheme. (lottery shopping no longer enjoys preferential treatment) the range of consumption amount x (yuan) 200 ≤ x < 400 ≤ x < 500 ≤ x < 700 The amount of lottery ticket (yuan) 30 60 100 According to the above promotion method, customers can get double discounts when shopping in the mall. If Mr. Hu gets a discount of 120 yuan when buying a household appliance in the mall, the price of the appliance is______ Yuan
17. On the formula of quadratic function
18. The ratio of lucky money for Party A and Party B is 4:3, and the ratio of money spent is 18:13. At this time, they all have 36 yuan left. How much did Party A and Party B have? Who gives me the wrong answer, I will not live First come first score ~ answer the correct plus score within five minutes!
19. 73,
20. My height is 1.56cm, weight 58kg is very fat? How many jin do I need to lose