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?

When the acceleration of the wood block is maximum, it should satisfy f = u1mg, then acceleration a = u1g, then the acceleration of the board should not be less than u1g, then the resultant force F = ma = mu1g = f - (f board + F ground) = f - [U1

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1. 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
2. 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?
3. 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!
4. 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?
5. 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?
6. As shown in the figure, a long board with mass m and length L is placed on the horizontal table, and a small wood block with mass m and length negligible is placed on the right end of the board. At the beginning, the wood block and board are static, and a constant horizontal right pulling force with the size of F direction is applied to the board from a certain moment, if the maximum static friction is equal to the sliding friction (1) If the ground is smooth and m and m are relatively stationary, what is the friction force on M? (2) If the dynamic friction coefficients between the wood block and the board, and between the board and the table top are μ, and the pulling force F = 4 μ (M + m) g, the time from the beginning of the movement to the time when the board is pulled out from under the small wood block is calculated
7. As shown in the figure, a long board with mass m and length L is placed on a smooth horizontal plane, and an object with mass m (regarded as a particle) rushes up to the board from the left end at a certain initial speed. If the long board is fixed, the object just stops at the right end of the board. If the long board is not fixed, the maximum distance that the object can slide on the board after it rushes up to the board is () A. LB. 3L4C. L4D. L2
8. As shown in the figure, the left end of a light spring is fixed on the left end of the long wooden board m2, and the right end is connected with the small wooden block M1, and the contact surface between M1 and M2, M2 and the ground is smooth. At the beginning, M1 and M2 are stationary. Now, the horizontal constant forces F1 and F2 are applied to M1 and m2 at the same time. In the whole process after the two objects start to move, the system composed of M1, M2 and the spring (spring deformation in the whole process) is analyzed No more than its elastic limit) A. Because of the reverse direction of F1 and F2, the mechanical energy of the system is conserved. B. because F1 and F2 do positive work for M1 and M2 respectively, the kinetic energy of the system increases continuously. C. Because F1 and F2 do positive work for M1 and M2 respectively, the mechanical energy of the system increases continuously. D. when the spring force is equal to F1 and F2, the kinetic energy of M1 and M2 is the largest
9. As shown in the figure, a and B plates are connected by a light spring, and their masses are M1 and M2 respectively How much pressure does it need to add on board a to stop the action of the force, which can make a slightly lift B when jumping up. (set the stiffness coefficient of the spring as K). Thank you ~ ~ the process is more detailed ~ ~ thank you~~ The picture shows a horizontal plate a above, a spring in the middle, and a horizontal plate B below. They are all connected~~
10. As shown in the figure, two objects with mass of M1 and M2 are connected by a light spring and placed on a rough inclined plane with an inclination angle of θ. The dynamic friction coefficient between the object and the inclined plane is μ. The pulling force parallel to the inclined plane and the size of F acts on M1 to make M1 and M2 move upward uniformly and accelerate, and the inclined plane is always stationary on the horizontal ground, then () A. The spring force is m2m1 + m2fb. The spring force is m2m1 + M2F + μ m2gsin θ C
11. 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
12. 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?
13. 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
14. 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
15. 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
16. 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
17. 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
18. 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?
19. 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
20. 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