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

We should pay special attention to this kind of problem, especially when it comes to decelerating, it will accelerate reversely after decelerating, involving the problem of vertical throwing up, the problem of conveyor belt goods braking in the car, etc., which needs careful thinking and solving process; v = 4m / s, a = 0.2m / S2, s = vt-1 / 2at2, T1 = 20-10 × root 2

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1. If the slope is 20 m long, how long does it take for a person to cross the top of the slope?
2. 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
3. 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
4. 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
5. 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
6. 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"?
7. 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
8. Why does the tension of the rope change suddenly while the spring and elastic rope can't change suddenly
9. 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?
10. 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?
11. 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．
12. 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?
13. 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?
14. 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?
15. 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?
16. If the vehicle with mass m runs on the straight road with constant power P, if the vehicle runs at constant speed V1, when the vehicle's speed is V2 (V2 < V1), the acceleration of the vehicle is () A. Pmυ1B. Pmυ2C. P(υ1−υ2)mυ1υ2D. Pυ1υ2m(υ1−υ2)
17. When a car is driving on a straight road, its acceleration direction is the same as the speed direction A. The speed of the car also decreases. B. the speed of the car is still increasing. C. when the acceleration decreases to zero, the car is stationary. D. when the acceleration decreases to zero, the speed of the car reaches the minimum
18. A 20 m long truck and a 6 m long car are driving at a speed of 20 m / s on a straight road at a constant speed. The distance between the two cars is 25 M. at present, the car overtakes at an acceleration of 0.5 m / S2. The car does not enter the lane from the overtaking lane until it exceeds 30 m of the truck
19. The bus departs from the station and runs at a speed of 4 m / s along the straight road at a constant speed. Two seconds later, a motorcycle departs from the same station to catch up at a constant speed The acceleration is 3m / S & sup2;, Q 【1】 How long does it take for the motorcycle to catch up with the car? 【2】 How far is it from the starting point when the motorcycle catches up with the car
20. A. Two cars B drive in the same direction on the straight road. Car a moves at a constant speed at the speed of VA = 20m / s, and car B moves at a constant deceleration straight line at the initial speed of vb0 = 24m / s, with the acceleration of a = 2m / S2. If car B is at △ s = 165m in front of car a, how long does it take for the two cars to meet? A student has the following solution: let two cars meet at the passing time t, then SA = VAT, sb = vb0t-12at2, SA = sb + △ s, The value of t can be obtained by combining the above formulas with the data. Do you think the student's solution is reasonable? If it is reasonable, please continue to calculate the time t; if not, please use your own method to calculate the correct result