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?

1. Kinetic energy theorem w = 1 / 2mv0 ^ 2-1 / 2mv1 ^ 2 = 1 / 2 * 0.02 * 600 ^ 2-1 / 2 * 0.02 * 400 ^ 2 = 3600-1600 = 2000j
2. The work done by external force with initial kinetic energy 2J is 8j, and the final kinetic energy 10J is not clear

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1. 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?
2. 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
3. The speed of a bullet hitting the board is 600 m / s, and it takes 0.001 s to get out of the board. The speed of a bullet passing through the board is 100 m / s The speed of a bullet hitting the board is 600 m / s, and it takes 0.001 s to get out of the board. The speed of a bullet passing through the board is 100 m / s. suppose that the bullet is decelerating and the mass of the bullet is 20 g. calculate the resistance of the bullet passing through the board and the thickness of the board
4. When a bullet with a mass of 10 g penetrates a board at a speed of 400 m / s and the speed becomes 100 m / s after passing through, the work done by the bullet to overcome the resistance is (1), If the thickness of the wood block is 10cm, the average resistance of the wood block to the bullet is (2) n. if the bullet can penetrate the cool wood block, the minimum velocity of the bullet is (3) m / s
5. A 2kg object a is placed on the light spring of the horizontal table. If a 3kg object B is placed on a lightly, the pressure of B on a is?
6. The light spring is upright and on the horizontal table. The object a with a mass of 2kg is placed on the top of the light spring in a static state. Now the object B with a mass of 3kg is placed on the table What is the elastic force of a to B at the moment when it is placed on a?
7. Under the action of a horizontal constant force F, an object with a mass of m on the horizontal plane starts to make a uniformly accelerated linear motion from rest. After time t, the external force is removed, and after time 2T, the object stops. What is the resistance of the object?
8. There is an object on a smooth horizontal plane. Under the action of horizontal constant force F, it starts to move from static state. After a certain period of time, its speed reaches V, and then after a period of time There is an object on a smooth horizontal plane, which starts to move from rest under the action of horizontal constant force F. after a certain period of time, the velocity reaches V, and then after a period of time, the velocity increases from V to 2V. In these two periods of time, what is the ratio of work done by external force F to the object?
9. Under the action of horizontal constant force F, the object with mass m starts to move along the horizontal plane from standstill. After t, the external force F is removed, and the object stops at the center after 2T (1) The resistance of the body (2) the total displacement of the body
10. Under the action of the horizontal constant force F, the object with mass m on the horizontal plane starts to make a uniformly accelerated linear motion from the static state, and the external force is removed after time t, and then the object moves after time 3T When the body stops, what is the resistance?
11. 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
12. 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
13. 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
14. 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
15. 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
16. 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
17. 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
18. 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
19. What are the factors related to the elongation of spring under the action of force
20. 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