A 3 kg block hangs from a light string passing over a frictionless pulley and pulls a 20 kg trolley along a horizontal surface (μk = 0.04, g = 10 m s⁻²). The acceleration of the system is:
A0.40 m s⁻²
B1.5 m s⁻²
C1.30 m s⁻²
D0.96 m s⁻²
Answer & Solution
Correct answer: D. 0.96 m s⁻²
Block: 3g − T = 3a. Trolley: T − μk N = 20a with N = 20×10 = 200 N, so μk N = 8 N. Adding: 30 − 8 = 23a ⟹ a = 22/23 ≈ 0.96 m s⁻². The distractors either ignore friction or mis-combine the masses.
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