On the ceiling, there are four balls with the same electric quantity, a, B, C and D, suspended by insulated thin wires. A and B are negatively charged, C and D are positively charged. They are close to the positively charged object M. affected by the charged body m, the thin wires deflect, as shown in the figure (1) By observing the sacrificial deflection of ball a and ball B, we can draw the following conclusions (2) By observing the sacrificial deflection of the C and D balls of the system, we can draw the following conclusions (2) Compare the string deflection angle of a, B or C, D balls, what rule can you guess?

(1) The positive and negative attract each other (2) the electrodes of the same name repel each other (3) the force between the two balls is inversely proportional to the distance between the two balls

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1. As shown in the figure, the two boards are sandwiched in the middle by baffles, and their masses are all m. calculate the friction between them
2. A long board of mass m is placed on a smooth horizontal surface A long board with mass m is placed on a smooth horizontal plane. A slider with mass m slides along the board surface from point a to point B at a certain speed v. it advances L on the board while the board advances S. if the dynamic friction coefficient between the slider and the board is μ, how much work does the friction force do to the slider and the board?
3. A long board with mass of M and length of L is placed on a smooth horizontal plane, and a small block with mass of M is placed at the rightmost end of the board Now add a horizontal constant force F to the right end of the long board, so that the long board is pulled out from under the small block, and the dynamic friction coefficient between the small block and the long board is μ, so as to find the work done by the horizontal constant force F to pull out the long board
4. As shown in the figure, on the inclined plane with an inclination angle of α, put a small ball with a mass of M, and the ball is blocked by a vertical board. Without friction, what are the pressures of the ball on the baffle and the inclined plane?
5. 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?
6. 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?
7. 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
8. 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
9. 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
10. 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
11. Hang two balls a and B at the same point o on the horizontal ceiling with two thin wires of the same length, connect two balls a and B with the same length, and then apply force F on ball a, as shown in the figure. At this time, the three thin wires are in a straight state, and ob thin wire is just in the vertical direction, and the two balls are in a static state. Regardless of the size of the ball, the possible direction of force F is zero Xiang Wei () A. Horizontal right B. vertical up C. along o → a direction D. along B → a direction
12. The upper end of a light spring is fixed on the ceiling of the elevator, and an object is suspended at the lower end When the elevator is stationary, the spring elongation is 8 cm; later, it is found that the spring elongation is 12 cm. According to this, the movement of the elevator at this time may be () A. the acceleration is g / 2 B. The acceleration is g / 2 C. The acceleration is 3G / 2
13. The elevator is suspended with a spring scale on the ceiling, and a small ball is hung under the spring scale. When the elevator moves, the reading of the spring scale becomes larger Then why is the elevator moving downward to make uniform deceleration or upward to make uniform acceleration
14. What is the indication when the two ends of the spring dynamometer are pulled by different forces? For example, 5N force at one end and 6N force at the other
15. What is the reading of the physical spring Dynamometer when both sides are pulled with 5N force? What is the reading with 10N force on both sides? What is the reading with 5N force on one side without force? Why
16. What is the indication of both ends of a spring dynamometer with the same force? For example, if two forces are 5N, why is the indicator also 5N instead of adding or subtracting (composition / decomposition of forces)?
17. The two hands pull the spring scale with 6N force respectively. What is the indication of the spring scale?
18. Use both hands to pull a spring scale with 10N force at the same time, why is the indication still 10N? I don't understand that. Who knows? Explain
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