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
Let the mass of the bullet be m, and apply the kinetic energy theorem to the whole process of the bullet passing through AB: 12mvb2-12mva2 = WF, because the friction force on the bullet remains unchanged, and because the length of a is l and the length of B is 2L, the work done by the friction force in the process of the bullet passing through a is 13wf, and apply the kinetic energy theorem to the process of the bullet passing through a: 12mva12-12mva2 = 13wf, and the solution is va1 = 2v12 + v223
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- 2. 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?
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- 7. 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?
- 8. 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?
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