[Daily Question] Theoretical Basis 2020.02.26

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Multiple choice questions: Blocks A and B are stacked as shown in the figure, and friction is considered at each contact surface. When block B moves along the horizontal plane under the action of force F, block A is still stationary on block B, so ( ) A. The frictional force at each contact surface does negative work B. The frictional force at each contact surface does positive work C.A The friction force on the block does positive work DB The friction force on the block does positive work answer: C When two objects A and B move to the right under the action of force F, the friction force acting on block A is in the same direction as the movement of block A, and the friction force does positive work. ； The friction force acting on block B is opposite to the movement direction of block B, and the friction force does negative work. hint: Those who can explain the problem-solving process will be given extra rewards, and the answers will be visible in the reply!