The initial velocity of the object is 5m / s, and the acceleration is - 2m / S ^ 2 What is the distance in 4 seconds if you slide on a rough horizontal surface? Is the object moving in the direction of acceleration to the left or deceleration to the right

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• 1. Does the elasticity of spring and rope disappear immediately? Can the elasticity of spring be regarded as constant? Why does the book say that the spring force "can often be regarded as constant"?
• 2. About springs, rubber ropes and ropes! Isn't the tension constant at the moment when the spring and the rubber rope break? For example, when the rope and the spring are used to bolt a heavy object and a wooden pole respectively, the tension of the spring on it doesn't change at the moment when it is cut? Here is a question that is a little incomprehensible: "in children's bungee jumping," the elastic rubber rope tied to the left and right sides of the waist is excellent, The tension of the two rubber ropes is just Mg (that is, the angle between the two of the three ropes is 120 degrees). The moment when the rubber rope on Xiaoming's left side breaks () why is the answer: acceleration a = g, the direction is opposite to the original tension direction of the broken rubber rope? The speed keeps the same with the situation. But the analysis of acceleration means that the rubber rope on the left side breaks, and because of the instantaneous invariance of the rubber rope, So the tension of the right rubber rope is constant, so the acceleration is g, which is opposite to the original tension direction of the broken rubber rope. My idea is that the left rubber rope should also have instantaneous invariance? Please answer my question comprehensively
• 3. Why does the tension of the rope change suddenly while the spring and elastic rope can't change suddenly
• 4. Why is it that when the rope is stretched straight and breaks suddenly, the tension of the rope will disappear instantly, while when both sides of the spring are stretched with the rope (or compressed with other methods), when the rope is broken, or when other parts are relaxed, the elasticity of the spring will not disappear instantly?
• 5. A wooden box is placed on the horizontal ground. The gravity of the box is 4000N. Under the horizontal thrust of 2000N, the box moves forward at a speed of 0.5mgs for 10s (1) How far does the box go? (2) What is the work done by the thrust on the box in these 10 seconds?
• 6. The pulley block is used to pull the object a on the horizontal ground to move forward at a uniform speed of 5m within 10s. If the weight of the object is 10000n, the friction between the object and the ground is 200N, the mechanical efficiency of the pulley block is 80%, and the friction of the machine itself is not taken into account. To find out (1) how much work is done by the pulling force? How much extra work is done? (2) how much is the pulling force F? (3) how much is the pulling force power?
• 7. When an object moves eastward at a speed of 5 m / s for 6 m / s, and northward at a speed of 3 M / s for 4 S, the velocity of the object in the 10 s is the same What is the average speed.
• 8. If someone pulls a 100N object forward 5m on the horizontal ground with a 50N horizontal pulling force, the work done by the pulling force on the object is () the work done by gravity on the object ( Big brothers and sisters, help to solve this problem
• 9. When an object weighing 100N is pulled horizontally to the right by 20n and moves horizontally to the right at a constant speed for 5m, the work done by the pulling force is______ J. What does gravity do______ J. What is the resistance to an object______ N. Direction______ ．
• 10. Xiao Zhang uses a horizontal pull force of 30n to lift an object with a weight of 100N and make it move 5m horizontally. After that, the pull force does work J and the gravity does work J The explanation of gravity work,
• 11. When an object is accelerating uniformly, its initial velocity is 2 m / s, and its displacement in the third second is 4.5 m, the acceleration is calculated
• 12. An object moves in a straight line at a constant speed. After 12M, the speed changes from 4m / s to 2m / s. calculate the acceleration
• 13. When someone rides a bicycle up a slope at the initial speed of V0 = 10m / s, the acceleration is 0.4m/s2 during the uphill process, and the speed decreases to 2m / s when he reaches the top of the slope. The time taken for the person to ride a bicycle up the slope is calculated
• 14. If the slope is 20 m long, how long does it take for a person to cross the top of the slope?
• 15. The bicycle decelerates at an initial speed of four meters per second. The acceleration is 0.2. How long does it take to climb a 20 meter slope You know, big brother, big sister, uncle and aunt
• 16. When the car moves in a straight line at a speed of 10m / s on a straight road, if there is something in front of it and the acceleration is 2m / S2, the speed of the car at the end of 3S after braking is 2m / S2______ &The displacement of the vehicle in 6S is______ m．
• 17. When the car moves in a straight line at a speed of 10 m / s on a straight road, it brakes when there is something in front of it, and the acceleration is 2 m / S2 What is the speed of the car after 3 seconds? What is the speed of the car after 7 seconds?
• 18. The car is moving forward on the straight road at the speed of 10m / s, and it starts to brake at a certain moment. If the acceleration is 2m / S ^ 2, the displacement of the car in the next 6S will be reduced The size is a24m b25m c75m d96m. Why is 24m wrong?
• 19. On a straight road, the speed of a car is 15m / s, and it starts to brake at a certain moment. Under the action of resistance, the car moves at an acceleration of 2m / S2. How far is the last car from the starting braking point after 10s of braking?
• 20. The car starts to drive on the straight road from the standstill, and the graph of the car's acceleration changing with time within 60 s is as follows Can you tell me which formula to use?