A block of mass 3m can move without friction on a horizontal table. This block is attached to another block of mass m by a cord that passes over a frictionless pulley, as shown above. If the masses of the cord and the pulley are negligible, what is the magnitude of the acceleration of the descending block?
Correct answer: A. g/4
- A. g/4
- B. g/3
- C. 2g/3
- D. g
Explanation
To find the acceleration of the descending block, consider both masses as a single system. The gravitational force on mass m is the only force causing the system to accelerate. Applying Newton's Second Law, ΣF = ma, to the entire system gives mg = (4m)a. Solving for a, we find a = g/4. Option A is correct because it accurately uses the total mass of the system in the calculation. Options B, C, and D are incorrect due to errors in considering the force distribution or the system's total mass.
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