Two blocks are connected by a light string passing over a pulley. The block with mass m1 slides on the frictionless horizontal surface, while the block with mass m2 hangs vertically (m1 m2). The tension in the string is

Question

Two blocks are connected by a light string passing over a pulley. The block with mass m1 slides on the frictionless horizontal surface, while the block with mass m2 hangs vertically (m1 > m2). The tension in the string is

BlackTom AI · Accepted Answer

When two blocks are connected by a light string over a pulley, the system accelerates as a single unit with the hanging mass m2 providing the driving force. For the horizontal block m1 on a frictionless surface, the only horizontal force is the string tension T, while for the hanging mass m2, the forces are gravity m2 g downward and tension T upward.

Option A: less than m2g. This is plausible because the hanging mass accelerates downward, reducing the net tension in the rope below the full weight m2 g. In a system with acceleration, the tension is typically less than the weight of the hanging mass, so this option is consistent with expected dynamics.

Option B: equal to m2g. If T were equal to m2 g, the hanging mass would experience zero net force and would not accelerate. But the problem clearly describes an accelerating system (m1 > m2), so T cannot equal m2 g. This makes B incorrect.

Option C: equal to m1g. The horizontal block experiences tension T as the only horizontal force, but there is no need for T to balance m1 g; the horizontal surface provides no vertical involvement for T, and the acceleration relates T to both masses. Therefore T cannot equal m1 g in this setup, so C is incorrect.

Option D: greater than m1g. A tension greater than the weight of the horizontal block would imply an unrealistically large horizontal force relative to vertical forces and would not align with the energy/force balance in this frictionless scenario. Since the system accelerates due to m2 g, T stays below m2 g and well below m1 g in this configuration, ruling out D as well.

In summary, for this arrangement with m1 > m2 on a frictionless surface, the tension is less than the weight of the hanging mass and less than m1 g, leading to the conclusion that the correct description is that T is less than m2 g.

Two blocks are connected by a light string passing over a pulley. The block with mass m1 slides on the frictionless horizontal surface, while the block with mass m2 hangs vertically (m1 > m2). The tension in the string is 单项选择题

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