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As shown in the figure, the mass ratio of a and B is Ma: MB = 3:2. They were originally stationary on the flat car C. There is a compressed spring between a and B. the dynamic friction coefficient between a and B and the upper surface of the flat car is the same, and the ground is smooth. When the spring is suddenly released, there is () A. A, B, C system momentum conservation B. A, B system momentum conservation C. car remains stationary D. car moves to the right
A. If the ground is smooth and the combined external force of a, B and C system is zero, the momentum of the system is conserved, so a is correct; B. because Ma: MB = 3:2, the friction force of a and B is different, so the combined external force of a and B system is not zero, and the momentum is not conserved, so B is wrong; C. because the mass ratio of a and B is Ma: MB = 3:2, known from the friction formula F = μ n = μ mg, a is right for the car Before a and B stop moving relative to the car, the resultant force of the car will move to the left, so CD is wrong
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