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?

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• 1. 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?
• 2. 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!
• 3. Description of the speed of movement The X -- t images of three objects moving in a straight line are compared 1. Displacement size:---- 2. Distance:---- 3. Average speed:-----
• 4. There is a high-speed camera to take a picture of the moment when the bullet penetrates the apple. After zooming in, it is found that the distance between the front and back of the bullet image is about 1% - 2% of the length of the bullet in the exposure time. It is known that the flight speed of the bullet is about 500m / s, so it can be estimated that the exposure time of this picture is the closest () A) 10's negative third second B) 10's negative sixth second C) 10's negative ninth second D) 10's negative twelfth second Although this problem is completely solved, I can't understand the answer, so please do it and explain it yourself Where did the bullet come from when it was five centimeters long?
• 5. A wooden raft drifts along the river. When the wooden raft passes through a wharf, a motorboat just goes down the wharf to the village 15km away from the wharf. After 0.75h, it arrives at the village and returns immediately. Then it meets the wooden raft 9km away from the village to calculate the flow rate of the river and the speed of the boat in still water
• 6. River width d = 100m, water speed V1 = 5m / s, ship speed V2 = 3m / s in still water, the shortest voyage of the ship across the river, the shortest voyage way to cross the river time
• 7. Two small balls are fixed at both ends of a rod with length L, and make a circular motion around a point o on the rod. The speed of small ball 1 is V1, and the speed of small ball 2 is v2. Calculate the distance from O to 2
• 8. The same object moves at the speed of V1 for the first time and V2 for the second time on the same plane (V1 > V2). Why is the pulling force the same when the moving speed is different?
• 9. When an object is thrown horizontally from a certain height, the initial velocity is 3m / s, the landing velocity is 5m / s, and the air resistance is not considered
• 10. A small ball is thrown horizontally at the speed of 3m / s, and its landing speed is 5m / s. The time and displacement of the ball in the air are calculated
• 11. 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?
• 12. 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?
• 13. 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?
• 14. 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
• 15. 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
• 16. 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
• 17. 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
• 18. 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?
• 19. 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
• 20. 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