Mass of the heavier block, m1 = 3 kg
Mass of the lighter block, m2 = 2 kg
Let the tension in the string be T and acceleration in the system be a.
According to the diagram,
T = m1a + m1g ⇒ T = 2(g+a)
m2g = T + m2a ⇒ T = 3(g-a)
⇒ a= g/5 m/s2
We need to find work done by gravity in the fourth second.
⇒ Time, t = 4 s
Change in height, h = 1/2 a(2t-1) (From equations of motion)
Work done by gravity = (m2-m1)×g×h
= (3-2) × 9.8 × 6.86
= 67.228 N
≈ 67 N
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