Under the condition of the same force, which factors of the spring will affect the length of the spring extension? 1. Guess one: the material of the spring will affect the elongation of the spring Conjecture 2: the length of the spring will affect the elongation of the spring Guess 3: the length of the spring will affect the elongation of the spring 2. Please design an experimental scheme to verify the conjecture

1. Guess the length and thickness of the second and third
2. Take several springs with the same length and thickness, but different materials, hang hook codes with the same quality at one end, and observe the change of length

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1. Under the action of force F, an object with mass m = 10kg moves at an acceleration of a = 2m / s for 2m on the horizontal ground with dynamic friction coefficient μ = 0.2. Try to find the work done by force F on the object and the work done by the object to overcome the resistance
2. The board with mass m is fixed on a smooth horizontal plane. The bullet with mass m flies horizontally through the block at the speed V0 and the speed is V0 / 2. Now the block is not fixed and can slide on the smooth horizontal plane. The same bullet hits the block at the initial speed V0 in the horizontal direction. If M < 3M, then the bullet: A. Can shoot through a block of wood B. Can not shoot through the block, stay in the block to move together C. It just penetrates the block, but it stays at the edge of the block and moves together
3. As shown in the figure, bullet a does not pass through the stationary wood block B on the smooth horizontal ground, then the system composed of a and B () A. Conservation of momentum, conservation of mechanical energy B. conservation of momentum, non conservation of mechanical energy C. The kinetic energy reduced by the bullet is equal to the kinetic energy increased by the block D. the kinetic energy reduced by the bullet is greater than the kinetic energy increased by the block
4. As shown in the figure, on a smooth horizontal plane, the bullet horizontally enters the wood block and remains in the wood block. Now, the bullet, spring and wood block are taken as the research object. In the whole process from the bullet's entry into the wood block to the shortest compression of the spring, the system () A. Conservation of energy, non conservation of mechanical energy B. non conservation of energy, non conservation of mechanical energy C. conservation of both energy and mechanical energy D. non conservation of energy, non conservation of mechanical energy
5. The left end of the wood block with mass m (which can be regarded as a mass) is connected with a light spring, and the other end of the spring is connected with a baffle fixed on a large enough smooth horizontal table The left end of the wood block with mass m (which can be regarded as a mass point) is connected with a light spring, the other end of the spring is connected with a baffle fixed on a large enough smooth horizontal table, the right end of the wood block is connected with a light thin line, which bypasses the smooth light pulley without mass, and the wood block is in a static state. In the following cases, the spring is within the elastic limit, regardless of air resistance and line deformation, The acceleration of gravity is g (1) In figure a, a constant force of F is applied at the other end of the line. The block leaves the initial position o and moves to the right. The spring begins to stretch and deform. It is known that the speed of the block passing through point P is V, and the distance between two points OP is S. the elastic potential energy of the spring when the block is pulled to point P is calculated; (2) If at one end of the line, instead of applying a constant force, a hook code with mass m is suspended, as shown in Figure B, the block moves from the initial position o to the right, and the speed of the block passing through point P is calculated
6. When the bullet hits the wooden block resting on the smooth horizontal table at a certain speed, the depth of the bullet into the wooden block is xcm, and the distance of the wooden block moving relative to the table is xcm, the ratio of the heat energy generated by the friction between the bullet and the wooden block and the kinetic energy lost by the bullet is 0
7. As shown in the figure, the wood blocks a and B are side by side and fixed on the horizontal table. The length of a is l, and the length of B is 2L. A bullet enters a at the speed V1 along the horizontal direction and passes out B at the speed v2. The bullet can be regarded as a particle, and its motion can be regarded as a uniform linear motion. Then the velocity of the bullet passing through a is () A. 2(v12+v22) 3B. 2(v12+v22) 3C. 2v12+v223D. v12+2v223
8. The bullet with a mass of 0.02kg penetrates a fixed plank with a thickness of 10cm vertically at a speed of 600mgs. It is known that the velocity of the bullet passing through the plank is 400m/ Find the work done by the resistance of the board to the bullet (2) When an object with mass m = 1kg moves on a smooth horizontal line, the initial velocity V1 = 2m / s, and is subjected to a combined external force F = 4N in the same direction as the motion, the displacement S = 2m, what is the final kinetic energy of physics?
9. The bullet with mass m of 0.02kg vertically penetrates a fixed board with thickness s of 10cm at the speed V1 of 600m / s, It is known that the average resistance of the board to the bullet is 2x10000. What is the velocity of the bullet after passing through the board?
10. The velocity of a bullet hitting the board is 600 m / s and the duration is 0.001 S & nbsp; the velocity of a bullet passing through the board is 100 m / s. suppose that the bullet passing through the board is a uniform deceleration motion, try to find: (1) the acceleration of the bullet passing through the board. (2) the thickness of the board
11. What are the factors related to the elongation of spring under the action of force
12. A. The masses of two objects B are m and 2m respectively, which are the same as the dynamic friction coefficient between the horizontal ground. Now, the same horizontal force F is applied to the two objects which are both static. If the acceleration speed of object a is a, then the acceleration of object B is a
13. As shown in the figure, a wooden board is still on a smooth and long horizontal plane, with mass m = 4kg and length L = 1.4m; at the right end of the board, there is a small slider n with mass m = 1kg, whose size is far less than l, and the dynamic friction coefficient between the small slider and the wooden block μ = 0.4 & nbsp; (g = 10m / S2). (1) in order to make n slide down from m, we use constant force F to act on M? (2) Other conditions remain unchanged, if constant force F = 22.8n, and is always used on M, n can finally slide down from M. Q: how long does n slide on M?
14. There is a board standing on a smooth horizontal plane, with mass of M = 4kg and length of L = 1.4m. At the right end of the board, there is a small block which can be regarded as a particle, with mass of M = 1kg, friction coefficient of u = 0.4 and g = 10m / S ^ 2. Now, the leveling force F acts on the board and makes m slide down from M. what is the minimum value of F?
15. On the smooth horizontal plane, there is a wooden board with L = 4m and M = 3kg mass (excluding thickness), and a small object with M = 1kg mass is placed on the rightmost side of the board The dynamic friction coefficient between M and M is u = 0.1. Now, a horizontal right pulling force F.G = 10m / s ＾ 2 is applied to the board. Find (1) how much f can't exceed in order to prevent the small object from sliding relative to the board? (2) if the pulling force F = 10N, how long does it take for the small object to fall off the board?
16. The object with mass of M = 1kg is placed on the inclined plane of 37, as shown in the figure. The dynamic friction coefficient between the object and the inclined plane is u = 0.3, if the object and the inclined plane are in the horizontal direction together An object with a mass of M = 1kg is placed on the inclined plane of 37. As shown in the figure, the dynamic friction coefficient between the object and the inclined plane is u = 0.3. If the object and the inclined plane accelerate to the left along the horizontal direction, what is the acceleration?
17. The object with mass m = 1kg is placed on the inclined plane with an inclination angle of 37. The mass of the inclined plane is 2kg. The dynamic friction coefficient between the inclined plane and the object is 0.2. The ground is smooth. Now, a horizontal thrust is applied to the inclined plane. As shown in the figure, to make the object m relative to the inclined plane stationary, the value range of the force F? Let the maximum static friction between the object and the inclined plane equal to the sliding friction
18. As shown in the figure, the mass of an object m = 2kg is at point a on the inclined plane with an inclination angle of θ = 37 ° When the object reaches B, the spring will be compressed to point C with the maximum compression BC = 0.2m, and then the object will be bounced up again by the spring. The highest position of bounce is point D, and the distance between point D and point a is ad = 3M. The mass of baffle and spring is not included, and g = 10m / S ^ 2, sin37 ° = 0.6, Find: (1) the dynamic friction coefficient μ between the object and the inclined plane. (2) the maximum elastic potential energy E of the spring
19. As shown in the figure, the board with length L = 1.6m and mass m = 3kg is placed on a smooth horizontal plane, the small block with mass m = 1kg is placed on the right end of the board, and the dynamic friction coefficient between the board and the block μ = 0.1. Now, apply a horizontal right tension f to the board, take g = 10m / S2, and find: (1) the maximum tension f to keep the block from falling; (2) if the tension f = 10N is constant, the maximum friction coefficient of the small block can be obtained Maximum speed
20. As shown in the figure, a long board with a mass of M = 3kg is parked on a smooth horizontal plane, and a small block with a mass of M = 1kg is placed on the board. At a certain moment, after the two blocks and the board simultaneously obtain the initial velocity of V = 4m / S in the opposite direction, they begin to move in the opposite direction. It is known that there is friction between the boards, (1) the speed and direction of the final board and block; (2) when the board moves to the right at the speed of 2.4m/s, the speed and direction of the block