a. B and C are the same three fast wood blocks, which are fixed on the horizontal plane side by side. When a bullet is fired along the horizontal direction, it can just shoot through the three wood blocks The time ratio of the three pieces of wood

In fact, this is the problem of equal displacement time ratio of uniform acceleration linear motion. For uniform acceleration linear motion with zero initial velocity, the ratio of displacement in 1t, 2T, 3T is S1: S2: S3... Sn = 1 square: 2 square: 3 square: n square. The ratio of instantaneous velocity in 1t, 2T, 3T is V1: V2: V3...: VN = 1

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1. As shown in the figure, the bullet with mass m penetrates the wood block on the smooth horizontal ground horizontally at the speed of V 0. The length of the wood block is l, the mass is m, and the resistance of the wood block to the bullet is constant. After the bullet passes through the wood block, the kinetic energy of the wood block is EK. If only the mass of the wood block or bullet changes, but the bullet can still pass through the wood block, then () A. If M is constant and M becomes smaller, the kinetic energy obtained by the wood block will certainly increase. If B. m is constant and M becomes smaller, the kinetic energy obtained by the wood block may increase. If C. m is constant and M becomes smaller, the kinetic energy obtained by the wood block will certainly increase. If D. m is constant and M becomes smaller, the kinetic energy obtained by the wood block may increase
2. When the wood block with mass m = 3M is fixed on a smooth horizontal plane, a bullet with mass m is fired into the wood block along the horizontal direction at the velocity V0, and the velocity of the bullet passing through the wood block is V03; now when the same wood block is placed on a smooth horizontal plane, and the same bullet is still fired into the wood block along the horizontal direction at the velocity V0, the bullet () A. It can't shoot through the wood block, the bullet and the wood block move at the same speed. B. It can shoot through the wood block. C. It can just shoot through the wood block, and the speed of the bullet is 0d. It can just shoot through the wood block, and the speed of the bullet is greater than V03
3. When a bullet with a mass of 10G hits a wooden block with a mass of 24g at a horizontal speed of 300m / s, if the bullet stays in the wooden block, what is the speed of the wooden block? (2) If the bullet penetrates the block, and the speed of the bullet is 100 m / s, what is the speed of the block?
4. The mass m bullet penetrates the m object suspended in the rope length L with V0, and the velocity V is used to calculate the tension of the rope
5. As shown in the figure, a board of mass m is placed on the board of mass M. the friction number between the board and the block is U1, and the board and the floor are connected The friction coefficient between the surfaces is U2. What is the horizontal force F applied on the board before the board can be pulled out from under the block?
6. As shown in the figure, the wood block P with mass m slides on the long board AB with mass m, and the long board is still on the horizontal ground. If the dynamic friction coefficient between the long board AB and the ground is μ 1, and the dynamic friction coefficient between the wood block P and the long board AB is μ 2, the friction force of the long board AB on the ground is () A. μ1MgB. μ1（m+M）gC. μ2mgD. μ1Mg+μ2mg
7. There is a wood block with mass m on the board with mass M. the dynamic friction factor between the board and the wood block is μ 1 The dynamic friction factor between the board and the horizontal ground is μ 2. What is the force F on the board before the board can be pulled out from under the board?
8. As shown in the figure, two identical wooden blocks are clamped by vertical wooden boards to keep static. If the mass of each block is m, the friction force between the two blocks is Please analyze in detail, thank you!
9. The mass of the long board is m = 100kg, the dynamic friction coefficient between the small block and the ground is U1 = 0.1, the mass of the small block is m = 100kg, and it starts to slide right on the long board from the left end at the initial speed V0 = 6m / s. The dynamic friction coefficient between the small block and the long board is U2. If the small block slides on the long board and the long board does not move, what conditions does U2 meet? What is the stress condition?
10. As shown in the figure, the masses of the two blocks are m respectively. M is connected with a light spring with a spring stiffness coefficient of K to prevent the block 1 from falling on the horizontal ground for a certain distance As shown in the figure, the masses of the two objects are m, and M is a light spring with spring stiffness coefficient K When the wooden block 1 is pressed down for a certain distance and released, it will move up and down in simple harmonic motion. In the process of vibration, the wooden block 2 will not leave the ground. Then the maximum acceleration of block 1 is shown as? What is the maximum pressure of block 2 on the ground?
11. When the mass of the bullet is m, the displacement of the bullet and the block relative to the ground is S1 and S2 respectively, then S1: S2 () A. M+2mmB. 2M+mMC. M+mmD. Mm
12. On the smooth horizontal plane, two blocks a and B with the same mass m and thickness d are arranged side by side. A bullet C with mass m shoots at the two blocks at the horizontal velocity v0 On the smooth horizontal plane, there are two identical blocks a and B with mass m and thickness d side by side. A bullet C with mass m shoots at two blocks with horizontal velocity v0. The velocity of the bullet after passing through the first block a is V0 / 2. The bullet is finally embedded in the second block B. what is the final velocity of the two blocks
13. 3. The square block with mass m and thickness d is statically placed on a smooth horizontal plane. As shown in the figure, a bullet with mass m penetrates the block horizontally at the initial velocity V0, and the resistance of the bullet is f and remains unchanged. In the process of the bullet penetrating the block, the displacement of the block is L. what are the velocities of the bullet and the block after the bullet passes through the block?
14. A bullet with mass m hits a wooden block with mass m resting on a smooth horizontal plane with velocity v0. The average resistance of the bullet in the wooden block is f, and the velocity of the bullet after penetrating the wooden block is V1. Find out (1) the velocity of the bullet penetrating the wooden block and (2) the displacement of the wooden block
15. As shown in the figure, the bullet with mass m hits the wooden block m resting on a smooth horizontal plane at the speed V0, and the average resistance of the bullet in the wooden block is f, The velocity of the bullet is v 1 after shooting through the block
16. As shown in the figure, the bullet with mass m penetrates horizontally at velocity V0 and is placed on a smooth horizontal plane The bullet with mass m penetrates horizontally at velocity V0 on a smooth horizontal plane If the block mass m, the bullet mass m or the bullet initial velocity V0 changes, but the bullet can still pass through the block, then (assuming that the resistance of the block to the bullet and the block length remain unchanged) () A. If M remains the same, m becomes smaller and V0 remains the same, the kinetic energy obtained by the block will certainly increase B. If M becomes smaller, m remains unchanged, and V0 remains unchanged, the kinetic energy lost by the bullet must be smaller C. If M is constant, M is constant, and V0 is smaller, the kinetic energy obtained by the wood block must be constant D. No matter how V0, m and M change, the mechanical energy loss of the system will remain unchanged
17. A. B: the mass ratio of the two objects Ma: MB = 1:2. Connect them with a spring without mass and place them on a smooth horizontal plane. Object a leans against the fixed plate, as shown in the figure. Push object B to the left and compress the spring. When the external force does work W, the external force is suddenly removed. After object a starts to move, the maximum elastic potential energy of the spring is () A. W3B. W2C. 2W3D. W
18. The ball with mass ma and MB is connected with light spring L1 and L2 with stiffness coefficient K as shown in the figure. When the two springs are at rest, the elongation is X1 and X2 respectively, then () A. As long as Ma = MB, there is X1 = x2b. As long as Ma > MB, there is X1 < X2C. As long as Ma < MB, there is X1 < x2d. As long as it does not exceed the elastic limit, there is always X1 > x2
19. As shown in the figure, a and B balls with mass ma and MB are connected by light spring, a ball is suspended by string, and both balls are in a static state. If the string hanging a ball is cut off, what are the instantaneous accelerations of a and B balls at this time?
20. Two small balls a and B with mass ma and MB are respectively connected to both ends of the spring, and the B end is fixed on a smooth inclined plane with an inclination of 30 ° by a thin line If the mass of the spring is not taken into account, the accelerations of balls a and B are 0 and [(MA + MB) / MB] · g / 2. B ball, I don't understand. How to analyze the force on the spring?